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1.
An Sist Sanit Navar ; 43(3): 297-306, 2020 Dec 22.
Article in Spanish | MEDLINE | ID: mdl-33057244

ABSTRACT

BACKGROUND: The electronic prescription systems implemented in the different autonomous communities in Spain show differences. This study aims to describe how these differences affect access to treatments and pharmaceutical care, and what specific characteristics facilitate them. METHODS: A survey was designed to evaluate the electronic prescription systems. This survey was carried out at the Drug Information Centers of the Official Pharmacists' Colleges of all the Spanish autonomous communities during February and March 2020. RESULTS: In all autonomous communities there were some limitations regarding the temporary availability of the treatment, and incidents regarding the way of accessing the electronic prescription were recorded only in only five communities. In no community are pharmacies able to solve availability problems in special circumstances, nor is there any effective system for communicating with the doctor or recording patient data. Only some communities organize certain replacements to adapt the prescription to the patient's requirements. CONCLUSIONS: The current electronic prescription system could be optimized to avoid inequalities between autonomous communities and improve the quality of care received by patients, facilitating access to treatments, and avoiding the need to travel and delays. Access on presenting the health card, adaptation of time limitations to avoid blockages, dispensing medicines in special circumstances justified and registered by the pharmacist, as well as enabling efficient pharmacist-doctor communication, are general measures that avoid inequalities and facilitate access to treatments and pharmaceutical care.


Subject(s)
Electronic Prescribing , Pharmaceutical Services , Health Services Accessibility , Humans , Pharmacists , Spain
2.
Diagn Microbiol Infect Dis ; 93(4): 334-338, 2019 Apr.
Article in English | MEDLINE | ID: mdl-30583880

ABSTRACT

Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis cases in the Ukraine are increasing. Pyrazinamide (PZA) is critically important for first- and second-line tuberculosis (TB) treatment regimes. However, PZA drug susceptibility testing is time consuming and technically challenging. The present study utilized Next-generation sequencing (NGS) to identify mutations in the pncA gene from clinical isolates and to assess the prevalence of pncA gene mutations in MDR/XDR-TB patients. Clinical isolates were inactivated in molecular transport media and shipped from Kharkiv, Ukraine, to San Antonio, TX. Whole-genome and targeted pncA gene sequencing was carried out using Illumina MiSeq instrumentation. Mutations were noted in 67 of 91 (74%) clinical isolates comprising substitutions, insertions, and deletions in the pncA coding and upstream promoter region. Of 45 mutation types, there were 11 novel, i.e., to date unknown, pncA mutations identified of which 3 were confirmed PZA resistant. Seven isolates contained mixed base mutations, whereas 4 harbored doubled mutations. Data reported here further support use of NGS for pncA gene characterization and may contribute in significant fashion to PZA therapy, especially in MDR- and XDR-TB patients.


Subject(s)
Amidohydrolases/genetics , Mutant Proteins/genetics , Mutation , Mycobacterium tuberculosis/enzymology , Mycobacterium tuberculosis/genetics , Tuberculosis, Multidrug-Resistant/microbiology , Genetic Variation , High-Throughput Nucleotide Sequencing , Humans , Mycobacterium tuberculosis/isolation & purification , Prevalence , Tuberculosis, Multidrug-Resistant/epidemiology , Ukraine/epidemiology
3.
J Clin Microbiol ; 56(6)2018 06.
Article in English | MEDLINE | ID: mdl-29563202

ABSTRACT

The Ukraine ranks among the top 20 countries with the highest number of multidrug-resistant (MDR) and extensively drug resistant (XDR) Mycobacterium tuberculosis cases in the world. However, little is known of the genetic diversity, i.e., resistance signatures, in clinical isolates from this region. We analyzed seven of most prevalent MDR/XDR antibiotic resistance-conferring genes from clinical isolates (n = 75) collected from geographically diverse Ukrainian oblasts and the southern Crimean peninsula. Genomic analysis revealed that 6 (8%) were sensitive, 3 (4%) were resistant to at least one antibiotic but were not MDR, 40 (53%) were MDR, and 26 (35%) were XDR. The majority of isolates (81%) were of the Beijing-like lineage. This is the first study to use next-generation sequencing (NGS) of clinical isolates from the Ukraine to characterize mutations in genes conferring M. tuberculosis drug resistance. Several isolates harbored drug resistance signatures that have not been observed in other countries with high-burden tuberculosis. Most notably, the absence of inhA gene promoter mutations, a diversity of mutation types in the rpoB resistance-determining region, and detection of heteroresistance provide a broader understanding of MDR/XDR from this area of the world.


Subject(s)
Extensively Drug-Resistant Tuberculosis/epidemiology , Genes, Bacterial , Genetic Variation , Mycobacterium tuberculosis/genetics , Tuberculosis, Multidrug-Resistant/epidemiology , Adult , Antitubercular Agents/pharmacology , Bacterial Proteins/genetics , DNA-Directed RNA Polymerases/genetics , Drug Resistance, Multiple, Bacterial/genetics , Extensively Drug-Resistant Tuberculosis/microbiology , Female , Genome, Bacterial , Genotype , High-Throughput Nucleotide Sequencing , Humans , Male , Microbial Sensitivity Tests , Middle Aged , Mutation , Mycobacterium tuberculosis/drug effects , Oxidoreductases/genetics , Promoter Regions, Genetic , Real-Time Polymerase Chain Reaction , Sequence Analysis, DNA , Sputum/microbiology , Tuberculosis, Multidrug-Resistant/microbiology , Ukraine/epidemiology
4.
J Dairy Sci ; 100(1): 106-112, 2017 Jan.
Article in English | MEDLINE | ID: mdl-27865504

ABSTRACT

Fast real-time PCR TaqMan assays were developed and validated for species identification in dairy products. Based on the amplification of 12S rRNA and cytB partial genes of mitochondrial DNA, the methods were demonstrated to be sensitive, fast, and species-specific for Bos taurus, Ovis aries, Bubalus bubalis, and Capra hircus. The limit of detection calculated was lower than 1%, and the efficiency was reported to be higher than 96% in every assay. An internal amplification control was used to detect possible false negatives. The method was validated by means of laboratory-prepared samples mixing different species. Moreover, 18 commercial dairy samples were analyzed by both real-time PCR and isoelectric focusing, the official European Union reference method. The 4 TaqMan assays were confirmed to be a useful tool for milk and dairy product authentication.


Subject(s)
Dairy Products/analysis , Food Analysis/methods , Milk/chemistry , Real-Time Polymerase Chain Reaction/methods , Animals , Buffaloes , Cattle , Goats , Limit of Detection , Sensitivity and Specificity , Sheep, Domestic , Species Specificity
5.
Int J Tuberc Lung Dis ; 20(8): 1118-24, 2016 08.
Article in English | MEDLINE | ID: mdl-27393549

ABSTRACT

BACKGROUND: The Xpert(®) MTB/RIF assay is widely used for Mycobacterium tuberculosis detection. However, specimen transport remains a challenge. PrimeStore Molecular Transport Medium(®) (PS-MTM) inactivates specimens and stabilizes DNA/RNA at ambient temperature for subsequent molecular detection. OBJECTIVE: To compare the detection of M. tuberculosis concentrations in PS-MTM using Xpert and real-time polymerase chain reaction (RT-PCR), and smear-positive sputum specimens collected using a flocked swab. METHODS: Dilutions of M. tuberculosis in PS-MTM and phosphate buffered saline (PBS) were analyzed using the Xpert assay and commercial RT-PCR. Smear-positive (1+ to 3+) sputum specimens (n = 17) were transferred by flocked swab into PS-MTM and PBS, and were compared to standard 1.0 ml sputum Xpert analysis. RESULTS: Using the Xpert assay, cycle threshold values from high M. tuberculosis concentrations in PS-MTM (>10(3) colony forming units [cfu]/ml) were increased compared to control. In contrast, M. tuberculosis samples containing <10(3) cfu/ml, i.e., low concentrations, suspended in PS-MTM resulted in detection down to 10 cfu/ml. Xpert detection efficiency in PS-MTM treated samples (63.2%) was improved compared to PBS controls (34.9%). Xpert detected M. tuberculosis in all sputum specimens collected by flocked swabs in PS-MTM, and correlated with routine Xpert detection. CONCLUSIONS: PS-MTM enhances M. tuberculosis detection at low concentrations of M. tuberculosis, and provides a simplified and efficient collection method for Xpert detection.


Subject(s)
Molecular Diagnostic Techniques , Mycobacterium tuberculosis/genetics , Real-Time Polymerase Chain Reaction , Specimen Handling/methods , Sputum/microbiology , Tuberculosis, Pulmonary/diagnosis , Humans , Mycobacterium tuberculosis/growth & development , Predictive Value of Tests , Reproducibility of Results , Retrospective Studies , Tuberculosis, Pulmonary/microbiology
7.
Clin Microbiol Infect ; 22(1): 59.e1-59.e8, 2016 Jan.
Article in English | MEDLINE | ID: mdl-26321668

ABSTRACT

Levofloxacin extended prophylaxis (LEP), recommended in oncohaematological neutropenic patients to reduce infections, might select resistant bacteria in the intestine acting as a source of endogenous infection. In a prospective observational study we evaluated intestinal emergence and persistence of ampicillin-resistant Enterococcus faecium (AREfm), a marker of hospital adapted high-risk clones. AREfm was recovered from the faeces of 52 patients with prolonged neutropenia after chemotherapy, at admission (Basal), during LEP, and twice weekly until discharge (Pos-LEP). Antibiotic susceptibility, virulence traits and population structure (pulsed-field gel electrophoresis and multilocus sequence typing) were determined and compared with bacteraemic isolates. Gut enterococcal population was monitored using a quantitative PCR quantification approach. AREfm colonized 61.4% of patients (194/482 faecal samples). Sequential AREfm acquisition (25% Basal, 36.5% LEP, 50% Pos-LEP) and high persistent colonization rates (76.9-89.5%) associated with a decrease in clonal diversity were demonstrated. Isolates were clustered into 24 PFGE-patterns within 13 sequence types, 95.8% of them belonging to hospital-associated Bayesian analysis of population structure subgroups 2.1a and 3.3a. Levofloxacin resistance and high-level streptomycin resistance were a common trait of these high-risk clones. AREfm-ST117, the most persistent clone, was dominant (60.0% isolates, 32.6% patients). It presented esp gene and caused 18.2% of all bacteraemia episodes in 21% of patients previously colonized by this clone. In AREfm-colonized patients, intestinal enrichment in the E. faecium population with a decline in total bacterial load was observed. AREfm intestinal colonization increases during hospital stay and coincides with enterococci population enrichment in the gut. Dominance and intestinal persistence of the ST117 clone might increase the risk of bacteraemia.


Subject(s)
Ampicillin/pharmacology , Anti-Bacterial Agents/pharmacology , Anti-Bacterial Agents/therapeutic use , Bacteremia/epidemiology , Enterococcus faecium/drug effects , Gram-Positive Bacterial Infections/epidemiology , Hematologic Neoplasms/complications , Levofloxacin/therapeutic use , Neutropenia/complications , beta-Lactam Resistance , Adult , Aged , Antibiotic Prophylaxis/adverse effects , Antibiotic Prophylaxis/methods , Bacteremia/microbiology , Blood/microbiology , Electrophoresis, Gel, Pulsed-Field , Enterococcus faecium/classification , Enterococcus faecium/genetics , Enterococcus faecium/isolation & purification , Feces/microbiology , Female , Humans , Male , Middle Aged , Molecular Typing , Prospective Studies , Real-Time Polymerase Chain Reaction , Risk Assessment
8.
Int J Tuberc Lung Dis ; 19(5): 552-7, 2015 May.
Article in English | MEDLINE | ID: mdl-25868023

ABSTRACT

SETTING: Mopani District, South Africa. OBJECTIVE: To explore remote, molecular detection of Mycobacterium tuberculosis from sputum transported using PrimeStore(®) Molecular Transport Medium (PS-MTM) compared to settings where microscopy or Xpert(®) MTB/RIF is used as the baseline test. DESIGN: Two sputum specimens were collected from patients with cough of ⩾ 2 weeks at clinics in rural South Africa. Shortly after expectoration and before processing using Xpert, microscopy and liquid culture, a flocked swab was swirled in each of these specimens and placed in PS-MTM. Swabs were stored and transported to the United States at ambient temperature for real-time PrimeMix(®) polymerase chain reaction (PM-PCR). RESULTS: Of 132 patients, 23 (17%) were positive on microscopy, 39 (30%) on Xpert and 44 (33%) by PS-MTM/PM-PCR. Concordance of PS-MTM/PM-PCR with positive microscopy and Xpert was respectively 96% and 85%. Of 107 microscopy-negative samples, 22 (21%) were positive using PS-MTM/PM-PCR, while 11/91 (12%) Xpert-negative samples were PS-MTM/PM-PCR-positive. PS-MTM/PM-PCR positivity was significantly higher than smear microscopy positivity (P < 0.001), but similar to Xpert (P = 0.33). CONCLUSION: PCR testing of specimens transported in PS-MTM would enhance TB diagnosis in settings where smear microscopy is the baseline diagnostic test, and could provide an alternative in settings where Xpert testing is not available.


Subject(s)
Mycobacterium tuberculosis/isolation & purification , Specimen Handling/methods , Sputum/microbiology , Telemedicine/methods , Tuberculosis, Pulmonary/diagnosis , Adult , Africa South of the Sahara , Aged , Aged, 80 and over , Cohort Studies , DNA, Bacterial/analysis , Extensively Drug-Resistant Tuberculosis/diagnosis , Extensively Drug-Resistant Tuberculosis/epidemiology , Female , Humans , Male , Middle Aged , Molecular Diagnostic Techniques , Mycobacterium tuberculosis/genetics , Prospective Studies , Real-Time Polymerase Chain Reaction/methods , Rural Population , Tuberculosis, Multidrug-Resistant/diagnosis , Tuberculosis, Multidrug-Resistant/epidemiology , Tuberculosis, Pulmonary/epidemiology , United States , Young Adult
10.
Int J Tuberc Lung Dis ; 18(7): 847-9, 2014 Jul.
Article in English | MEDLINE | ID: mdl-24902564

ABSTRACT

In many parts of the world, the diagnosis of tuberculosis (TB) has rapidly shifted to molecular detection and sequencing formats. The collection and transport of Mycobacterium tuberculosis specimens thus remains a challenging problem where TB is common and the infrastructure required for ensuring sample integrity is lacking. PrimeStore(®) Molecular Transport Medium (MTM) addresses this problem, rapidly inactivating/killing M. tuberculosis while preserving genomic DNA even at elevated temperatures for subsequent downstream molecular analysis.


Subject(s)
Molecular Diagnostic Techniques/methods , Mycobacterium tuberculosis/isolation & purification , Specimen Handling/methods , Tuberculosis/diagnosis , Bacteriological Techniques/methods , DNA, Bacterial/isolation & purification , Humans , Mycobacterium tuberculosis/genetics , Temperature , Tuberculosis/microbiology
11.
Phys Chem Chem Phys ; 16(8): 3757-62, 2014 Feb 28.
Article in English | MEDLINE | ID: mdl-24430097

ABSTRACT

The photodynamics of phenol-ammonia clusters, PhOH(NH3)(3-5), after one UV photon absorption, has been investigated using velocity map imaging of the NH4(NH3)(2-4) cluster products. The dependence of the NH4(NH3)2 translational energy distributions on the available energy reveals three dynamical regions in close correspondence with the photodissociation of bare phenol. At low excitation energies (between 282 and 260 nm), the NH4(NH3)2 distribution mirrors the hydrogen-atom passage through the 1(1)ππ*-1(1)πσ* barrier, constituting the first evidence of hydrogen-atom tunneling dynamics in an excited state hydrogen transfer (ESHT) reaction. At excitation wavelengths below 260 nm, the product distributions are consistent with two separate barrierless dissociation processes associated, respectively, with excitation to the 1(1)ππ* and 2(1)ππ* excited electronic states. Similar conclusions can be derived from the velocity map imaging results on the larger NH4(NH3)(3,4) cluster products.

13.
J Phys Chem A ; 117(34): 8175-83, 2013 Aug 29.
Article in English | MEDLINE | ID: mdl-23713854

ABSTRACT

The photodissociation of nitromethane at 193 nm is reviewed in terms of new stereodynamical information provided by the measurement of the first four Dixon's bipolar moments, ß0(2)(20), ß0(0)(22), ß0(2)(02), and ß0(2)(22), using slice imaging. The measured speed-dependent ß0(2)(20) (directly related with the spatial anisotropy parameter ß) indicates that after one-photon absorption to the S3(2 (1)A″) state by an allowed perpendicular transition, two reaction pathways can compete with similar probability, a direct dissociation process yielding ground-state CH3 and NO2(1 (2)A2) radicals and a indirect dissociation through conical intersections in which NO2 radicals are formed in lower-lying electronic states. A particularly important result from our measurements is that the low recoil energy part of the methyl fragment translational energy distribution presents a contribution with parallel character, irrespective of the experimental conditions employed, that we attribute to parent cluster dissociation. Moreover, the positive values found for the ß0(0)(22) bipolar moment indicates some propensity for the fragment's recoil velocity and angular momentum vectors to be parallel.

14.
J Chem Phys ; 137(9): 094305, 2012 Sep 07.
Article in English | MEDLINE | ID: mdl-22957567

ABSTRACT

The excited state hydrogen transfer (ESHT) reaction in pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-5) at excitation wavelengths below 218 nm down to 199 nm, has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(n-1) products. Special care has been taken to avoid evaporation of solvent molecules from the excited clusters by controlling the intensity of both the excitation and probing lasers. The high resolution translational energy distributions obtained are analyzed on the base of an impulsive mechanism for the hydrogen transfer, which mimics the direct N-H bond dissociation of the bare pyrrole. In spite of the low dissociation wavelengths attained (~200 nm) no evidence of hydrogen-loss statistical dynamics has been observed. The effects of clustering of pyrrole with ammonia molecules on the possible statistical decomposition channels of the bare pyrrole are discussed.

15.
Phys Chem Chem Phys ; 13(36): 16404-15, 2011 Sep 28.
Article in English | MEDLINE | ID: mdl-21847502

ABSTRACT

The photodissociation of CH(3)I in the blue edge (217-230 nm) of the A-band has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization (REMPI) detection of the CH(3) fragment in the vibrational ground state (ν = 0). The profiles of the CH(3) (ν = 0) kinetic energy distributions and the photofragment anisotropies are interpreted in terms of the contribution of the excited surfaces involved in the photodissociation process, as well as the probability of non-adiabatic curve crossing between the (3)Q(0) and (1)Q(1) states. In the studied region, unlike in the central part of the A-band where absorption to the (3)Q(0) state dominates, the I((2)P(J)), with J = 1/2, 3/2, in correlation with CH(3) (ν = 0) kinetic energy distributions show clearly two contributions of different anisotropy, signature of the competing adiabatic and non-adiabatic dynamics, whose ratio strongly depends on the photolysis wavelength. The experimental results are compared with multisurface wave packet calculations carried out using the available ab initio potential energy surfaces, transition moments, and non-adiabatic couplings, employing a reduced dimensionality model. A good qualitative agreement is found between experiment and theory and both show evidence of reverse (3)Q(0)←(1)Q(1) non-adiabatic dynamics at the bluest excitation wavelengths both in the fragment kinetic energy and angular distributions.

16.
J Chem Phys ; 135(2): 021102, 2011 Jul 14.
Article in English | MEDLINE | ID: mdl-21766918

ABSTRACT

The photodissociation of CH(3)I in the second absorption band (the B-band) has been studied at the wavelength 199.11 nm, coincident with the 3(0)(1) (3)R(1)(E)←X((1)A(1)) CH(3)I vibronic transition, using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the CH(3) fragment. The kinetic energy and angular distributions of the recoiling CH(3) fragment confirm a major predissociation dynamics channel as a result of the interaction between the bound (3)R(1) Rydberg state and the repulsive (3)A(1)(E) state--ascribed to the A-band--yielding CH(3) fragments in correlation with spin-orbit excited I*((2)P(1/2)) atoms. In addition, first evidence of a non-negligible population of ground state I((2)P(3/2)) atoms in the CH(3) fragment slice images, suggests a secondary predissociation mechanism via interaction between the (3)R(1) Rydberg state and the repulsive A-band (1)Q(1) state.

17.
J Anim Sci ; 89(8): 2472-84, 2011 Aug.
Article in English | MEDLINE | ID: mdl-21478455

ABSTRACT

The effects of type of grinding of barley and dehydrated alfalfa (DA) were tested in rabbits weaned at 35 d of age with an average BW of 846 ± 93 g. Four nonmedicated diets were arranged in a 2 × 2 factorial structure, with type of grinding (coarse grinding with a 4.5-mm screen or fine grinding with a 1.5-mm screen) of barley (TGB) and DA (TGDA) as the main factors. A total of 1,056 mixed-sex rabbits (264 per diet) were fattened until d 63. Most of these rabbits (216 per diet) were housed in pairs and were used only to record mortality rate. Mortality was also recorded for the remaining 192 rabbits, which were housed individually and used to determine growth performance. From this group, 100 rabbits were used to determine digestive traits. Apart from those rabbits, a different group of 88 rabbits (44 housed individually and the remaining 44 housed in pairs) was used in the digestibility trial. All rabbits in this group were used to determine ileal digestibility (13 pools of ileal digesta per diet) and ileal mucin concentration (6 pools of ileal digesta per diet), whereas only the 44 individually housed rabbits were used to assess the fecal digestibility coefficients (11 rabbits per diet). Last, a jejunal sample was excised from 32 of the 44 individually housed rabbits to determine mucosal histology. Treatments did not affect ADG, ADFI, or G:F in the entire fattening period, but in the 49- to 63-d period, the diet containing both finely ground barley and DA reduced ADFI (P=0.08) compared with the other treatments (130 vs. 137 g). Moreover, this diet increased total digestive tract (4.76%, P=0.08) and cecal content (11.3%, P=0.08) weights compared with the other 3 treatments. Pylorus (P=0.09) and mixed digesta (P=0.06) pH, respectively, were reduced from 1.53 and 1.59 to 1.37 and 1.44 when both barley and DA were finely instead of coarsely ground. Grinding both barley and DA coarsely reduced the ileal digestibility of starch (0.899 vs. 0.936, P=0.06), increased (P < 0.01) its ileal flow and content in the feces to 1.66 g/d and 7.42 g/kg of DM, respectively, and led to decreased fecal digestibility (0.932 vs. 0.951, P < 0.01) compared with fine grinding. Coarse DA shortened villi (612 vs. 704 µm, P=0.02), increased crypt depth (121 vs. 92.1 µm, P=0.01), and reduced the villus:crypt ratio (5.08 vs. 7.66, P < 0.01) compared with finely ground DA. Furthermore, the greatest ileal crude mucin (148 vs. 107 g/kg of DMI, P=0.02) and sialic acid (71.7 vs. 61.7 mg/kg of DMI, P=0.04) concentrations were reported in rabbits receiving the diet with both coarsely ground barley and DA. Finally, mortality rate was not influenced by treatments, with an average of 9.64%. In conclusion, the diet containing finely ground barley and coarsely ground DA did not increase the weight of cecal contents, resulting in increased feed intake and leading to increased ileal digestibility and reduced ileal flow of starch.


Subject(s)
Animal Feed/analysis , Digestion/physiology , Hordeum , Ileum/metabolism , Medicago sativa , Rabbits/growth & development , Animal Nutritional Physiological Phenomena , Animals , Cecum/microbiology , Clostridium perfringens , Diet/veterinary , Food Handling , Mucins/metabolism
18.
Phys Chem Chem Phys ; 13(18): 8186-94, 2011 May 14.
Article in English | MEDLINE | ID: mdl-21305088

ABSTRACT

The role of the conical intersection between the (1)Q(1) and (3)Q(0) excited states in the photodissociation of CH(3)I at 304 nm is investigated drawing a comparison between the adiabatic--through direct absorption to the (3)Q(1) state--and non-adiabatic--via the (1)Q(1)→(3)Q(0) conical intersection--production of I atoms in the ground (2)P(3/2) state. The versatility of the slice imaging technique in combination with resonance enhanced multiphoton ionization (REMPI) detection of I((2)P(3/2)) atoms allow distinct measurements of the competing processes. The I((2)P(3/2)) atom kinetic energy distributions (KEDs) obtained in both cases reflect inverted vibrational progressions of the ν(2) umbrella mode of the CH(3) co-product. The experimental results show a satisfactory agreement with multisurface wave packet calculations using a reduced dimensionality (pseudotriatomic) model carried out on the available ab initio potential energy surfaces.

19.
Phys Chem Chem Phys ; 13(3): 1082-91, 2011 Jan 21.
Article in English | MEDLINE | ID: mdl-21076731

ABSTRACT

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(n-1) products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (∼0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment.


Subject(s)
Ammonia/chemistry , Hydrogen/chemistry , Pyrroles/chemistry , Kinetics , Photolysis , Thermodynamics
20.
J Chem Phys ; 133(6): 064303, 2010 Aug 14.
Article in English | MEDLINE | ID: mdl-20707566

ABSTRACT

The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S(1), which, in turn, undergoes intersystem crossing to the first excited triplet state T(1). On the triplet surface, the molecule dissociates into CH(3) and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T(1). However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S(0) after internal conversion from S(1). We have characterized the fragments' KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T(1) is presented.

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