What are the experiences of non-invasive ventilation for sleep-disordered breathing in children and young people and what outcomes matter? Perspectives of children and young people, their parents and the staff who care for them.

BACKGROUND: Non-invasive ventilation (NIV) for sleep-disordered breathing (SDB) in children and young people (CYP) can result in multiple health outcomes; however, adherence to NIV can be challenging. Suboptimally treated SDB may increase the risk of adverse consequences. Placing children's and parents' goals at the core of their SDB treatment may support adherence to NIV. To identify these health outcomes, it is necessary to gain a greater understanding of CYP's experiences of using NIV, whether they perceive any benefits from NIV use, as well as the outcomes that their parents and NIV staff identify as important. METHODS: Semi-structured qualitative interviews were conducted with nine CYP (aged 4-16 + years), 13 parents and nine healthcare professionals (HCPs); verbatim transcripts were analysed using Framework Analysis. RESULTS: CYP predominantly reported an improvement in levels of energy, focus and ability to concentrate whereas parents also identified outcomes of mood and behaviour. The majority of children showed understanding of the reasons for being prescribed NIV. A subset of children did not notice their SDB. The health outcomes identified by HCPs and parents that could result from improved overnight gas exchange are subjective measures that rely on parent and child report. Measuring these health outcomes focussed on the impact of improved sleep rather than measuring improved sleep itself. CONCLUSIONS: It is important for HCPs administering NIV to ascertain whether CYP have noticed any of their sleep-disordered breathing symptoms and any improvements from using NIV, including the relationship between benefits and side effects. Focussing on promoting understanding for CYP who are unable to link their wellbeing to their previous night's sleep may be futile and HCP strategies should concentrate on the process of tolerating the device. Parents, CYP and HCPs should collaborate to identify treatment goals specifically tailored for the child and monitor any progress against these goals.

Ovarian cancer red flags: help prevent delayed diagnosis.

Ovarian cancer is classified as a gynaecological cancer, but the symptoms present as abdominal and they can be mistaken for those of a bowel condition or bladder problems. Target Ovarian Cancer is urging clinicians to recognise the red flags for ovarian cancer, and to never diagnose new-onset irritable bowel syndrome (IBS) or overactive bladder in women over 50 without ruling out ovarian cancer. The symptoms of these are also red flags for ovarian cancer and warrant further investigations. This article covers how to spot these red flags, safety netting and what to do if you suspect a woman's symptoms may be ovarian cancer.

Indoor Air Quality Implications of Germicidal 222 nm Light.

One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly promising approach is 222 nm light from KrCl excimer lamps (GUV222); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV222 on the composition of indoor air has received little experimental study. Here, we conduct laboratory experiments in a 150 L Teflon chamber to examine the formation of secondary species by GUV222. We show that GUV222 generates ozone (O3) and hydroxyl radicals (OH), both of which can react with volatile organic compounds to form oxidized volatile organic compounds and secondary organic aerosol particles. Results are consistent with a box model based on the known photochemistry. We use this model to simulate GUV222 irradiation under more realistic indoor air scenarios and demonstrate that under some conditions, GUV222 irradiation can lead to levels of O3, OH, and secondary organic products that are substantially elevated relative to normal indoor conditions. The results suggest that GUV222 should be used at low intensities and in concert with ventilation, decreasing levels of airborne pathogens while mitigating the formation of air pollutants.

What Happens When you Ask for Feedback? Anticipating and Addressing Challenges Can Be Effective for Eliciting Parents' Views About Their Critically Ill Child's Retrieval to Paediatric Intensive Care.

User feedback is an important element of health-service evaluation and can be used to improve services but can be difficult to obtain, particularly in acute care situations. As part of a national study, we explored stakeholders' perspectives on paediatric critical care retrieval processes through questionnaires and interviews. Obtaining feedback in a highly charged, stressful and busy paediatric intensive care unit (PICU) environment is fraught with difficulties so we aimed to optimise each stage of data collection by being both proactive and reactive. Patient and public involvement occurred throughout and engagement with sites and supporting local research staff to approach and recruit families were prioritised. High-quality study materials were developed to reduce local staff burden and promote and maintain study awareness. We describe strategies used and what worked/did not work. We suggest approaches for optimising elicitation of parents' experiences in difficult circumstances, highlighting the importance of engagement and commitment of PICU staff.

Is Parental Presence in the Ambulance Associated With Parental Satisfaction During Emergency Pediatric Intensive Care Retrieval? A Cross-Sectional Questionnaire Study.

OBJECTIVES: Quality standards for pediatric intensive care transport services in the U.K. state that at least one parent should be allowed to travel with their child during emergency transport to a PICU. We aimed to identify the reasons why parents do, or do not, accompany their child and whether there is an association between parental presence in the ambulance and their satisfaction with the transport. DESIGN: National cross-sectional parent questionnaire. SETTING: Pediatric Critical Care Transport (PCCT) teams and PICUs in England and Wales. PARTICIPANTS: Parents of children transferred to one of 24 participating PICUs between January 2018 and January 2019. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A parent feedback questionnaire was completed by parents whose child received an emergency interhospital transfer. As part of the questionnaire, a brief nine-item scale was developed to summarize parental transport experience (ranging from 1 to 5). The association between parental presence in the ambulance and parental experience was analyzed. A total of 4,558 children were transported during the study. Consent was obtained from 2,838 parents, and questionnaires received in 2,084 unique transports (response rate: 45.7%). In 1,563 transports (75%), at least one parent traveled in the ambulance. Parents did not travel in 478 transports (23%) and, in most instances (442 transports; 93%), offered reasons (emotional, practical, and health-related) for declining to travel or explanations why they were not permitted to travel (mainly due to space restrictions). Most parents rated their experience with the retrieval teams very highly, and within this context, we found evidence of greater variability in experience ratings if parents were not present in the ambulance and if this was not their choice. CONCLUSIONS: Most parents who completed questionnaires rated their experience with their PCCT team highly. Parental presence and choice to travel in the ambulance were associated with a more positive experience.

Development of a parent experience measure for paediatric critical care transport teams.

BACKGROUND: A third of children admitted to paediatric intensive care units (PICUs) in the United Kingdom (UK) are transported by paediatric critical care transport services (PCCTs). Parents have described the transfer journey as particularly stressful. Critical care nurses have a key role in mitigating the impact of the journey on parents. Evaluating parents' experiences is important to inform service improvements. AIM AND OBJECTIVES: Our aim was to describe the development of a new measure of parents' experiences of PCCTs, derived from data collected in the Differences in access to Emergency Paediatric Intensive Care and care during Transport (DEPICT) study. DESIGN: A descriptive cross-sectional survey was used. METHODS: As part of the DEPICT study, a 17-item transport experience questionnaire was developed and given to parents of children transported by PCCTs to 24 UK PICUs during a 12-month period. Analyses included exploratory factor analysis and a validation review by a PCCT stakeholder group. RESULTS: Families of 1722 children (1798 journeys) completed questionnaires. Five items were excluded from further analysis as correlation coefficients were <0.3. Two factors explained 53% of the variance and all 12 items loaded on one of these factors. Factor 1 (8 items) explained 47% of the variance, had excellent internal reliability and the clustered items were conceptually coherent with a specific relevance to PCCTs; these were offered for consideration, with other items possibly discarded. Twenty-eight PCCT clinicians reviewed the questions. Using a 70% agreement threshold, one additional, previously discarded, item was identified for inclusion, resulting in a nine-item experience measure. CONCLUSION: Our brief measure of parents' experience of critical care transport provides a standardized measure that can be used across all PCCTs, enabling national benchmarking of services and potentially increasing the collection and use of parent experience data to improve services. RELEVANCE TO CLINICAL PRACTICE: Being able to measure experience provides an opportunity to understand how to make services better to improve experience.

Chemistry of Functionalized Reactive Organic Intermediates in the Earth's Atmosphere: Impact, Challenges, and Progress.

The gas-phase oxidation of organic compounds is an important chemical process in the Earth's atmosphere. It governs oxidant levels and controls the production of key secondary pollutants, and hence has major implications for air quality and climate. Organic oxidation is largely controlled by the chemistry of a few reactive intermediates, namely, alkyl (R) radicals, alkoxy (RO) radicals, peroxy (RO2) radicals, and carbonyl oxides (R1R2COO), which may undergo a number of unimolecular and bimolecular reactions. Our understanding of these intermediates, and the reaction pathways available to them, is based largely on studies of unfunctionalized intermediates, formed in the first steps of hydrocarbon oxidation. However, it has become increasingly clear that intermediates with functional groups, which are generally formed later in the oxidation process, can exhibit fundamentally different reactivity than unfunctionalized ones. In this Perspective, we explore the unique chemistry available to functionalized organic intermediates in the Earth's atmosphere. After a brief review of the canonical chemistry available to unfunctionalized intermediates, we discuss how the addition of functional groups can introduce new reactions, either by changing the energetics or kinetics of a given reaction or by opening up new chemical pathways. We then provide examples of atmospheric reaction classes that are available only to functionalized intermediates. Some of these, such as unimolecular H-shift reactions of RO2 radicals, have been elucidated only relatively recently, and can have important impacts on atmospheric chemistry (e.g., on radical cycling or organic aerosol formation); it seems likely that other, as-yet undiscovered reactions of (multi)functional intermediates may also exist. We discuss the challenges associated with the study of the chemistry of such intermediates and review novel experimental and theoretical approaches that have recently provided (or hold promise for providing) new insights into their atmospheric chemistry. The continued use and development of such techniques and the close collaboration between experimentalists and theoreticians are necessary for a complete, detailed understanding of the chemistry of functionalized intermediates and their impact on major atmospheric chemical processes.

Screening for New Pathways in Atmospheric Oxidation Chemistry with Automated Mechanism Generation.

In the Earth's atmosphere, reactive organic carbon undergoes oxidation via a highly complex, multigeneration process, with implications for air quality and climate. Decades of experimental and theoretical studies, primarily on the reactions of hydrocarbons, have led to a canonical understanding of how gas-phase oxidation of organic compounds takes place. Recent research has brought to light a number of examples where the presence of certain functional groups opens up reaction pathways for key radical intermediates, including alkyl radicals, alkoxy radicals, and peroxy radicals, that are substantially different from traditional oxidation mechanisms. These discoveries highlight the need for methods that systematically explore the chemistry of complex, functionalized molecules without being prohibitively expensive. In this work, automated reaction network generation is used as a screening tool for new pathways in atmospheric oxidation chemistry. The reaction mechanism generator (RMG) is used to generate reaction networks for the OH-initiated oxidation of 200 mono- and bifunctionally substituted n-pentanes. The resulting networks are then filtered to highlight the reactions of key radical intermediates that are fast enough to compete with traditional atmospheric removal processes as well as "uncanonical" processes which differ from traditionally accepted oxidation mechanisms. Several recently reported, uncanonical atmospheric mechanisms appear in the RMG dataset. These "proof of concept" results provide confidence in this approach as a tool in the search for overlooked atmospheric oxidation chemistry. Several previously unreported reaction types are also encountered in the dataset. The most potentially atmospherically important of these is a radical-carbonyl ring-closure reaction that produces a highly functionalized cyclic alkoxy radical. This pathway is proposed as a promising target for further study via experiments and more detailed theoretical calculations. The approach presented herein represents a new way to efficiently explore atmospheric chemical space and unearth overlooked reaction steps in atmospheric oxidation.

Changing knowledge, attitudes and behaviours towards cytomegalovirus in pregnancy through film-based antenatal education: a feasibility randomised controlled trial of a digital educational intervention.

BACKGROUND: Congenital cytomegalovirus (CMV) is the most common congenital infection globally, however information about CMV is not routinely included in antenatal education in the United Kingdom. This feasibility study aimed to gather the essential data needed to design and power a large randomised controlled trial (RCT) to investigate the efficacy of a digital intervention in reducing the risk of CMV acquisition in pregnancy. In order to do this, we carried out a single-centre RCT, which explored the knowledge, attitudes and risk reduction behaviours in women in the intervention and treatment as usual groups, pre- and post-intervention. METHODS: CMV seronegative women living with a child less than four years old, receiving antenatal care at a single UK tertiary centre, were randomised to the digital intervention or 'treatment as usual' groups. Participants completed questionnaires before the digital intervention and after and at 34 gestational weeks, and responses within groups and between groups were compared using tailored randomisation tests. CMV serology was tested in the first trimester and at the end of pregnancy. RESULTS: Of the 878 women screened, 865 samples were analysed with 43% (n = 372) being CMV seronegative and therefore eligible to take part in the RCT; of these, 103 (27.7%) women were enrolled and 87 (84%) of these completed the study. Most participants (n = 66; 64%) were unfamiliar with CMV at enrolment, however at 34 gestational weeks, women in the intervention group (n = 51) were more knowledgeable about CMV compared to the treatment as usual group (n = 52) and reported engaging in activities that may increase the risk of CMV transmission less frequently. The digital intervention was highly acceptable to pregnant women. Overall, four participants seroconverted over the course of the study: two from each study group. CONCLUSIONS: A large multi-centre RCT investigating the efficacy of a CMV digital intervention is feasible in the United Kingdom; this study has generated essential data upon which to power such a study. This single-centre feasibility RCT demonstrates that a digital educational intervention is associated with increase in knowledge about CMV and can result in behaviour change which may reduce the risk of CMV acquisition in pregnancy. TRIAL REGISTRATION: Clinicaltrials.gov, NCT03511274 , Registered 27.04.18, http://www.Clinicaltrials.gov.

Understanding pregnant women's readiness to engage in risk-reducing measures to prevent infections during pregnancy.

The aim of this study was to develop a conceptual understanding of women's readiness to engage in behaviours to reduce the risk of acquiring infections during pregnancy, using cytomegalovirus, the most common congenital infection as a case. Thirty-three pregnant women participated in semi-structured interviews. The findings illustrate that for behavioural change to become viable, it is necessary for individuals to consider barriers or facilitators at the individual, inter-personal and system levels. By widening the theoretical lens beyond individual cognitive determinants, the model places sufficient emphasis on factors, such as collective identity, support networks, interaction with the healthcare system and wider community, relevant to pregnant women.

Parenting a child with congenital cytomegalovirus infection: a qualitative study.

BACKGROUND: Congenital cytomegalovirus (CMV) is the most common infectious cause of congenital disability, which can cause lifelong impairments including sensorineural hearing loss and developmental delay. This study aimed to explore the experiences of parenting a child with congenital CMV and the impact this has on families. METHODS: Ten parents living with a child with congenital CMV in the UK participated in semistructured interviews and data were analysed using thematic analysis. RESULTS: The findings illustrate that delays in making the diagnosis of congenital CMV are associated with parental distress and lack of knowledge about CMV among medical professionals can exacerbate this distress. Parents expressed frustration about not knowing about CMV infection during their pregnancies and therefore not having the opportunity to take measures to reduce their risk of acquiring CMV while pregnant. The uncertainty about the long-term outcomes of children with congenital CMV adds additional emotional burden for parents. Family and wider societal networks have the potential to facilitate coping and alleviate stress, but the lack of awareness of CMV acts as a barrier to receiving support from family and friends. CONCLUSIONS: There is a need to increase awareness of CMV among medical professionals, pregnant women and wider society to improve the diagnostic process and to provide better support for families caring for children with congenital CMV infection.

Prevention of Acquisition of Cytomegalovirus Infection in Pregnancy Through Hygiene-based Behavioral Interventions: A Systematic Review and Gap Analysis.

BACKGROUND: Congenital cytomegalovirus infection is the most common nongenetic cause of sensorineural hearing loss in childhood and an important cause of neurodisability. There is no licensed cytomegalovirus (CMV) vaccine and no antenatal treatment for congenital CMV that is routinely recommended in clinical practice in the United Kingdom. OBJECTIVES: To review the published literature for studies that evaluated preventative hygiene-based interventions in pregnancy for their impact on knowledge about CMV prevention, the uptake of preventative behaviors or the acquisition of CMV in pregnancy. SEARCH STRATEGY: Searches were carried out in Medical Literature Analysis and Retrieval System Online and Cumulative Index of Nursing and Allied Health Literature databases. SELECTION CRITERIA: All human studies, limited to women of childbearing age were included. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed the quality of the methods and results of included articles. Extracted data were classified using Cochrane guidelines. MAIN RESULTS: Seven studies met the inclusion criteria. These show that preventative measures are acceptable to pregnant women, can impact their behavior and have the potential to reduce CMV in pregnancy. They are limited by several factors; sample size, nonrandomized trial design and interventions that are beyond routine clinical practice. CONCLUSIONS: An effective intervention that changes behavior in pregnancy and reduces the risk of CMV acquisition is needed as part of routine care. There is currently insufficient evidence about the form that this intervention should take. REGISTRATION: PROSPERO registration number: CRD42017069666.

Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products.

The infrared (IR) action spectrum of the doubly substituted methyl-ethyl Criegee intermediate (MECI) is observed in the CH stretch overtone region with detection of OH products. The MECI exhibits four conformers, all of which undergo unimolecular decay via a 1,4 H-atom transfer mechanism, followed by the rapid release of OH products. Conformers with different orientations of the carbonyl oxide group with respect to the methyl and ethyl substituents (i.e., anti and syn) decay via distinct transition state barriers (16.1 kcal mol-1 and 15.4 kcal mol-1, respectively). The observed IR action spectrum is in good agreement with the predicted anharmonic IR absorption spectrum, but exhibits significant congestion, which is attributed to couplings between spectroscopic bright states and nearby dark states. Energy-dependent OH appearance rates are measured upon IR excitation of the strongest features in the IR action spectrum and are found to be on the order of 106-107 s-1. The experimental rates are in good agreement with computed Rice-Ramsperger-Kassel-Marcus rates for the unimolecular decay of MECI at these energies, which incorporate quantum mechanical tunneling and sophisticated hindered rotor treatments, as well as high-level theoretical calculations of the TS barrier heights, rovibrational properties, and torsional barriers associated with the MECI conformers. Master equation modeling is used to predict thermal rates for the unimolecular decay of anti- and syn-MECI of 473 s-1 and 660 s-1, respectively. Comparison with other previously studied Criegee intermediate systems provides insights into substituent effects on unimolecular decay under both energy-dependent and thermal conditions.

CH Stretch Activation of CH3CHOO: Deep Tunneling to Hydroxyl Radical Products.

Alkene ozonolysis, an important source of hydroxyl (OH) radicals in the Earth's troposphere, proceeds through unimolecular decay of Criegee intermediates. In this work, infrared activation of the methyl-substituted Criegee intermediate, syn-CH3CHOO, in the CH stretch fundamental region (2850-3150 cm-1) is shown to result in unimolecular decay to OH radical products. These excitation energies correspond to only half of the transition state barrier height, and thus the resultant 1,4 H atom transfer that leads to OH products occurs exclusively by quantum mechanical tunneling. Infrared action spectra recorded with UV laser-induced fluorescence detection of the OH products reveal the four CH stretch fundamentals and CO stretch overtone predicted to have strong transition strength. The vibrational band origins, relative intensities, and transition types derived from rotational band contour analyses are in good accord with theory. Distinctly different Lorentzian line broadening of the observed features is attributed to mode-specific anharmonic couplings predicted theoretically between spectroscopically bright and nearby dark states. The measured OH product state distribution shows a strong λ-doublet preference arising from pπ orbital alignment, which is indicative of the vinyl hydroperoxide intermediate along the reaction pathway. The unimolecular decay of syn-CH3CHOO at ca. 3000 cm-1 is predicted to be quite slow (ca. 105 s-1) using statistical Rice-Ramsperger-Kassel-Marcus theory with tunneling and much slower than observed at higher energies.

Nonparametric High-Resolution Coherent 3D Spectroscopy as a Simple and Rapid Method for Obtaining Excited-State Rotational Constants.

A new method for generating high-resolution coherent 3D (HRC3D) spectra has been developed that is based on the nonparametric four-wave mixing process MENS (multiply enhanced nonparametric spectroscopy). The resulting spectra have rotational patterns that are different from those produced previously using the parametric four-wave mixing process CARS. A change in the rotational pattern facilitates a new approach to scanning where orthogonal 2D slices in 3D space are combined to make a 3D rotational pattern. This 3D rotational pattern may then be used to calculate rotational constants for levels in the excited electronic state and upper regions of the ground electronic state. Unlike previous forms of HRC3D spectroscopy, this new approach provides a stand-alone rapid and simple tool for the rotational analysis of electronic spectra without the need for obtaining peak positions or molecular constants from other (1D or 2D) forms of spectroscopy.

Four-Carbon Criegee Intermediate from Isoprene Ozonolysis: Methyl Vinyl Ketone Oxide Synthesis, Infrared Spectrum, and OH Production.

The reaction of ozone with isoprene, one of the most abundant volatile organic compounds in the atmosphere, produces three distinct carbonyl oxide species (RR'COO) known as Criegee intermediates: formaldehyde oxide (CH2OO), methyl vinyl ketone oxide (MVK-OO), and methacrolein oxide (MACR-OO). The nature of the substituents (R,R' = H, CH3, CH═CH2) and conformations of the Criegee intermediates control their subsequent chemistry in the atmosphere. In particular, unimolecular decay of MVK-OO is predicted to be the major source of hydroxyl radicals (OH) in isoprene ozonolysis. This study reports the initial laboratory synthesis and direct detection of MVK-OO through reaction of a photolytically generated, resonance-stabilized monoiodoalkene radical with O2. MVK-OO is characterized utilizing infrared (IR) action spectroscopy, in which IR activation of MVK-OO with two quanta of CH stretch at ca. 6000 cm-1 is coupled with ultraviolet detection of the resultant OH products. MVK-OO is identified by comparison of the experimentally observed IR spectral features with theoretically predicted IR absorption spectra. For syn-MVK-OO, the rate of appearance of OH products agrees with the unimolecular decay rate predicted using statistical theory with tunneling. This validates the hydrogen atom transfer mechanism and computed transition-state barrier (18.0 kcal mol-1) leading to OH products. Theoretical calculations reveal an additional roaming pathway between the separating radical fragments, which results in other products. Master equation modeling yields a thermal unimolecular decay rate for syn-MVK-OO of 33 s-1 (298 K, 1 atm). For anti-MVK-OO, theoretical exploration of several unimolecular decay pathways predicts that isomerization to dioxole is the most likely initial step to products.

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products.

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH3CHOO. IR excitation of selectively deuterated syn-CD3CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn-CD3CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, which is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of ∼10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. At 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn-CH3CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of ∼50.

Tunneling effects in the unimolecular decay of (CH3)2COO Criegee intermediates to OH radical products.

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH3)2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer [Y. Fang et al., J. Chem. Phys. 144, 061102 (2016)] with time-resolved detection of the resultant OH radical products. (CH3)2COO is prepared at specific energies in the 3900-4600 cm-1 region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity of the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH3)2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH3)2COO to OH products under atmospheric conditions of 276 s-1 at 298 K (high pressure limit). Thermal unimolecular decay of (CH3)2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.

Deep tunneling in the unimolecular decay of CH3CHOO Criegee intermediates to OH radical products.

Unimolecular decay of Criegee intermediates produced in alkene ozonolysis is known to be a significant source of OH radicals in the troposphere. In this work, unimolecular decay of the methyl-substituted Criegee intermediate, syn-CH3CHOO, to OH products is shown to occur at energies significantly below the transition state barrier for a 1,4 hydrogen transfer that leads to these products [Y. Fang et al., J. Chem. Phys. 144, 061102 (2016)]. The rate of appearance of OH products arising from tunneling through the barrier is obtained through direct time-domain measurements following the vibrational activation of syn-CH3CHOO. IR excitation of syn-CH3CHOO at energies nearly 2000 cm-1 below the barrier is achieved through combination bands involving CH stretch and another lower frequency mode, and the resultant OH products are detected by UV laser-induced fluorescence. The observed syn-CH3CHOO combination bands in the 4100-4350 cm-1 region are identified by comparison with the computed IR absorption spectrum. The experimental decay rates are found to be ca. 106 s-1 in this deep tunneling regime, which is approximately 100-times slower than that in the vicinity of the barrier.The experimental results are consistent with statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical decay rates with tunneling through the barrier, and notable deviations may originate from the sparsity in the density of states for syn-CH3CHOO at lower energies. Thermal unimolecular decay of syn-CH3CHOO is predicted to have significant contribution from microcanonical rates at energies that are much below the barrier.