High-resolution infrared spectroscopy of jet cooled CH2Br radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling.

Direct laser absorption of a slit supersonic discharge expansion provides the first high-resolution spectroscopic results on the symmetric CH stretch excitation (ν1) of the bromomethyl (CH2Br) radical in the ground electronic state. Narrowband (<1 MHz) mid-infrared radiation is produced by difference-frequency generation of two visible laser beams, with the open shell halohydrocarbon radical generated by electron dissociative attachment of CH2Br2 in a discharge and rapidly cooled to Trot = 18 ± 1 K in the subsequent slit-jet supersonic expansion. A rovibrational structure in the radical spectrum is fully resolved, as well as additional splittings due to spin-rotation effects and 79Br/81Br isotopologues in natural abundance. Spectroscopic constants and band origins are determined by fitting the transition frequencies to a non-rigid Watson Hamiltonian, yielding results consistent with a vibrationally averaged planar radical and an unpaired electron in the out-of-plane pπ orbital. Additionally, extensive satellite band structure from a vibrational hot band is observed and analyzed. The hot band data is compared to CFOUR/VPT2 (CCSD(T)cc-pVQZ) ab initio anharmonic predictions of the vibration rotation alpha matrix, which permits unambiguous assignment to CH2 symmetric-stretch excitation built on the singly excited CH2 out-of-plane bending mode (ν1 + ν4 ← ν4). Longitudinal cooling of the Doppler width in the slit-jet expansion geometry also reveals partially resolved hyperfine structure on transitions out of the lowest angular momentum states in excellent agreement with predictions based on microwave studies. High level ab initio MOLPRO calculations [CCSD(T)-f12b/VnZ-f12 (n = 3, 4, CBS)] are also performed with explicitly correlated f12 electron methods for the out-of-plane CH2 bending mode over the halogen series CH2X (X = F, Cl, Br, I), which clearly reveals a non-planar geometry for X = F (with a ΔE ≈ 0.3 kcal/mol barrier) and yet planar equilibrium geometries for X = Cl, Br, and I. Finally, a detailed Boltzmann analysis of the transition intensities provides support for negligible collisional equilibration of the entangled H atom nuclear spin states on the few hundred microsecond time scale and high collision densities of a slit supersonic expansion.

Correction: Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν3/ν4 CH stretch modes and CH2 internal rotor dynamics of benzyl radical.

Correction for 'Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν3/ν4 CH stretch modes and CH2 internal rotor dynamics of benzyl radical' by A. Kortyna et al., Phys. Chem. Chem. Phys., 2017, 19, 29812-29821.

High-resolution infrared spectroscopy of jet cooled trans-deuteroxycarbonyl (trans-DOCO) radical.

The rovibrational spectrum of jet cooled trans-deuteroxycarbonyl (trans-DOCO) radical has been explored at suppressed-Doppler resolution via direct infrared absorption spectroscopy. The trans-DOCO is produced in a supersonic slit discharge of rare-gas/CO mixture doped with D2O, whereby the OD forms an energized adduct with CO, cooling in the supersonic expansion and stabilizing DOCO in the trans well. Active laser-frequency stabilization and collisional quenching of Doppler broadening along the slit axis yield <10 MHz frequency precision, with the absorbance noise approaching the quantum shot-noise limit. The current high-resolution spectral results are in excellent agreement with recent studies of the trans-DOCO radical by infrared frequency comb spectroscopy under room temperature conditions [Bui et al., Mol. Phys. 116, 3710 (2018)]. Combined with previous microwave/millimeter wave rotational studies, the suppressed-Doppler infrared data permit characterization of the vibrational ground state, improved structural parameters for the OD stretch vibrational level, and trans-DOCO spin-rotation information in both ground and excited vibrational states. Additionally, the infrared data reveal a-type and much weaker b-type contributions to the spectrum, analysis of which yields orientation of the OD stretch transition dipole moment in the body fixed frame. Of dynamical interest is whether the nascent trans-DOCO complex formed in the entrance channel has sufficient time to convert into the cis-DOCO isomer, or whether this is quenched by rapid stabilization into the trans-DOCO well. Ab initio and Rice-Ramsperger-Kassel-Marcus analysis of the intrinsic reaction coordinate for trans-DOCO to cis-DOCO interconversion rates supports the latter scenario, which helps explain the failure of previous high resolution infrared efforts to detect cis-hydroxycarbonyl.

Infrared spectroscopy of jet-cooled HCCl singlet chlorocarbene diradical: CH stretching and vibrational coupling dynamics.

Quantum shot noise limited laser absorption methods are used to obtain first high-resolution infrared rovibrational spectra of jet cooled chlorocarbene (HCCl) diradical in a supersonic slit-jet discharge expansion spectrometer. The rotationally resolved absorption spectra of the C-H stretch ν1 fundamental are analyzed in the framework of a Watson non-rigid asymmetric rotor Hamiltonian model. Further analysis of the mid-infrared data reveals the additional presence of what has nominally been assigned as the X̃(012) combination band with one quantum of the H-C-Cl bend (ν2) and two quanta of the C-Cl stretch (2ν3). Rovibrational constants are obtained from least squares fits for each of the four excited vibrational states built on the ν1 fundamental X̃(100) and the X̃(012) combination mode for each 35Cl and 37Cl atom isotopologue. The four bands occur within a narrow spectral window, requiring detailed comparison of multiple spectral properties (e.g., rotational constant dependence on vibrational excitation, band types/transition dipole moment alignment in the body-fixed frame, etc.) to aid in the vibrational assignment. Indeed, the IR transition intensities arise from strong anharmonic mixing between the "bright" ν1 C-H stretch and "dark" X̃012 H-C-Cl bend/C-Cl stretch combination modes, resulting in nearly equal amplitudes for the zeroth order X̃(100) and X̃012 harmonic states. Finally, to aid the spectral search for HCCl in the interstellar medium, ground state two-line combination differences are combined with previous laser-induced fluorescence results to predict precision microwave transitions for HC35Cl and HC37Cl.

High-resolution sub-Doppler infrared spectroscopy of atmospherically relevant Criegee precursor CH2I radicals: CH2 stretch vibrations and "charge-sloshing" dynamics.

The combination of a pulsed supersonic slit-discharge source and single-mode difference frequency direct absorption infrared spectroscopy permit first high resolution infrared study of the iodomethyl (CH2I) radical, with the CH2I radical species generated in a slit jet Ne/He discharge and cooled to 16 K in the supersonic expansion. Dual laser beam detection and collisional collimation in the slit expansion yield sub-Doppler linewidths (60 MHz), an absolute frequency calibration of 13 MHz, and absorbance sensitivities within a factor of two of the shot-noise limit. Fully rovibrationally resolved direct absorption spectra of the CH2 symmetric stretch mode (ν2) are obtained and fitted to a Watson asymmetric top Hamiltonian with electron spin-rotation coupling, providing precision rotational constants and spin-rotation tensor elements for the vibrationally excited state. Analysis of the asymmetric top rotational constants confirms a vibrationally averaged planar geometry in both the ground- and first-excited vibrational levels. Sub-Doppler resolution permits additional nuclear spin hyperfine structures to be observed, with splittings in excellent agreement with microwave measurements on the ground state. Spectroscopic data on CH2I facilitate systematic comparison with previous studies of halogen-substituted methyl radicals, with the periodic trends strongly correlated with the electronegativity of the halogen atom. Interestingly, we do not observe any asymmetric CH2 stretch transitions, despite S/N ≈ 25:1 on strongest lines in the corresponding symmetric CH2 stretch manifold. This dramatic reversal of the more typical 3:1 antisymmetric/symmetric CH2 stretch intensity ratio signals a vibrational transition moment poorly described by simple "bond-dipole" models. Instead, the data suggest that this anomalous intensity ratio arises from "charge sloshing" dynamics in the highly polar carbon-iodine bond, as supported by ab initio electron differential density plots and indeed consistent with observations in other halomethyl radicals and protonated cluster ions.

Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν3/ν4 CH stretch modes and CH2 internal rotor dynamics of benzyl radical.

Highly reactive benzyl radicals are generated by electron dissociative attachment to benzyl chloride doped into a neon-hydrogen-helium discharge and immediately cooled to Trot = 15 K in a high density, supersonic slit expansion environment. The sub-Doppler spectra are fit to an asymmetric-top rotational Hamiltonian, thereby yielding spectroscopic constants for the ground (v = 0) and first excited (v = 1, ν3, ν4) vibrational levels of the ground electronic state. The rotational constants obtained for the ground state are in good agreement with previous laser induced fluorescence measurements (LIF), with vibrational band origins (ν3 = 3073.2350 ± 0.0006 cm-1, ν4 = 3067.0576 ± 0.0006 cm-1) in agreement with anharmonically corrected density functional theory calculations. To assist in detection of benzyl radical in the interstellar medium, we have also significantly improved the precision of the ground state rotational constants through combined analysis of the ground state IR and LIF combination differences. Of dynamical interest, there is no evidence in the sub-Doppler spectra for tunneling splittings due to internal rotation of the CH2 methylene subunit, which implies a significant rotational barrier consistent with partial double bond character in the CC bond. This is further confirmed with high level ab initio calculations at the CCSD(T)-f12b/ccpVdZ-f12 level, which predict a zero-point energy corrected barrier to internal rotation of ΔEtun ≈ 11.45 kcal mol-1 or 4005 cm-1. In summary, the high-resolution infrared spectra are in excellent agreement with simple physical organic chemistry pictures of a strongly resonance-stabilized benzyl radical with a nearly rigid planar structure due to electron delocalization around the aromatic ring.

State-resolved velocity map imaging of surface-scattered molecular flux.

This work describes a novel surface-scattering technique which combines resonance enhanced multiphoton ionization (REMPI) with velocity-map imaging (VMI) to yield quantum-state and 2D velocity component resolved distributions in the scattered molecular flux. As an initial test system, we explore hyperthermal scattering (E(inc) = 21(5) kcal mol(-1)) of jet cooled HCl from Au(111) on atomically flat mica surfaces at 500 K. The resulting images reveal 2D (v(in-plane) and v(out-of-plane)) velocity distributions dominated by two primary features: trapping/thermal-desorption (TD) and a hyperthermal, impulsively scattering (IS) distribution. In particular, the IS component is strongly forward scattered and largely resolved in the velocity map images, which allows us to probe correlations between rotational and translational degrees of freedom in the IS flux without any model dependent deconvolution from the TD fraction. These correlations reveal that HCl molecules which have undergone a large decrease in velocity parallel to scattering plane have actually gained the most rotational energy, reminiscent of a dynamical energy constraint between these two degrees of freedom. The data are reduced to a rotational energy map that correlates with velocity along and normal to the scattering plane, revealing that exchange occurs primarily between rotation and the in-plane kinetic energy component, with v(out-of-plane) playing a relatively minor role.

A dipolar gas of ultracold molecules.

Ultracold polar molecular gases promise new directions and exciting applications in collisions and chemical reactions at ultralow energies, precision measurements, novel quantum phase transitions, and quantum information science. Here we briefly discuss key experimental requirements for observing strong dipole-dipole interactions in an ultracold dipolar gas of molecules. We then survey current experimental progress in the field with a focus on our recent work creating a near quantum degenerate gas of KRb polar molecules [Ni et al., Science, 2008, 322, 231].

Ultrasensitive ultraviolet-visible 20 fs absorption spectroscopy of low vapor pressure molecules in the gas phase.

We describe an ultrasensitive pump-probe spectrometer for transient absorption measurements in the gas phase and in solution. The tunable UV pump and the visible (450-740 nm) probe pulses are generated by two independently tunable noncollinear optical parametric amplifiers, providing a temporal resolution of 20 fs. A homebuilt low gain photodetector is used to accommodate strong probe pulses with a shot noise significantly lower than the overall measurement noise. A matched digitizing scheme for single shot analysis of the light pulses at kilohertz repetition rates that minimizes the electronic noise contributions to the transient absorption signal is developed. The data processing scheme is optimized to yield best suppression of the laser excess noise and thereby transient absorbance changes down to 1.1 x 10(-6) can be resolved. A collinear focusing geometry optimized for a 50 mm interaction length combined with a heatable gas cell allows us to perform measurements on substances with low vapor pressures, e.g., on medium sized molecules which are crystalline at room temperature. As an application example highlighting the capability of this instrument, we present the direct time-domain observation of the ultrafast excited state intramolecular proton transfer of 2-(2(')-hydroxyphenyl)benzothiazole in the gas phase. We are able to compare the resulting dynamics in the gas phase and in solution with a temporal precision of better than 5 fs.

Quantum state resolved scattering dynamics of F+HCl-->HF(v,J)+Cl.

State-to-state reaction dynamics of the reaction F+HCl-->HF(v,J)+Cl have been studied under single-collision conditions using an intense discharge F atom source in crossed supersonic molecular beams at Ecom=4.3(1.3) kcal/mol. Nascent HF product is monitored by shot-noise limited direct infrared laser absorption, providing quantum state distributions as well as additional information on kinetic energy release from high resolution Dopplerimetry. The vibrational distributions are highly inverted, with 34(4)%, 44(2)%, and 8(1)% of the total population in vHF=1, 2, and 3, respectively, consistent with predominant energy release into the newly formed bond. However, there is a small [14(1)%] but significant formation channel into the vHF=0 ground state, which is directly detectable for the first time via direct absorption methods. Of particular dynamical interest, both the HF(v=2,J) and HF(v=1,J) populations exhibit strongly bimodal J distributions. These results differ significantly from previous flow and arrested-relaxation studies and may signal the presence of microscopic branching in the reaction dynamics.

High-resolution IR studies of hydrogen bonded clusters: large amplitude dynamics in (HCl)n.

Structural and dynamical information on small hydrogen-bonded systems is revealed by high-resolution IR spectroscopy of HCl dimer, trimer and tetramer. In (HCl)2, four combination bands tentatively assigned to the Van der Waals stretch nu 4 and geared band nu 5 vibrations are observed. The study focuses on two unexpected results: (i) all of the observed bands are built only on the bound HCl stretch nu 2, and (ii) the bands predominantly originate from the 9-fold less populated upper tunneling level of the ground state. Model 3D quantum calculations are presented to show that both these surprising trends originate from the large amplitude tunneling dynamics in the dimer. The (HCl)3 spectra are assigned and analyzed for multiple isotopomeric contributions. The spectral fit reveals large homogeneous line broadening indicating the excited state lifetime of approximately 1.6 ns and tentatively associated with dynamics of intramolecular vibrational energy distribution (IVR) induced trimer ring opening. Finally, first high-resolution data on the HCl stretch fundamental spectrum of (HCl)4 are presented.

Inhibition of choroidal neovascularization by intravenous injection of adenoviral vectors expressing secretable endostatin.

Endostatin is a cleavage product of collagen XVIII that inhibits tumor angiogenesis and growth. Interferon alpha2a blocks tumor angiogenesis and causes regression of hemangiomas, but has no effect on choroidal neovascularization (CNV). Therefore, inhibitors of tumor angiogenesis do not necessarily inhibit ocular neovascularization. In this study, we used an intravenous injection of adenoviral vectors containing a sig-mEndo transgene consisting of murine immunoglobulin kappa-chain leader sequence coupled to sequence coding for murine endostatin to investigate the effect of high serum levels of endostatin on CNV in mice. Mice injected with a construct in which sig-mEndo expression was driven by the Rous sarcoma virus promoter had moderately high serum levels of endostatin and significantly smaller CNV lesions at sites of laser-induced rupture of Bruch's membrane than mice injected with null vector. Mice injected with a construct in which sig-mEndo was driven by the simian cytomegalovirus promoter had approximately 10-fold higher endostatin serum levels and had nearly complete prevention of CNV. There was a strong inverse correlation between endostatin serum level and area of CNV. This study provides proof of principle that gene therapy to increase levels of endostatin can prevent the development of CNV and may provide a new treatment for the leading cause of severe loss of vision in patients with age-related macular degeneration.

Field enhancement in apertureless near-field scanning optical microscopy.

The near field of an apertureless near-field scanning optical microscopy probe is investigated with a multiple-multipole technique to obtain optical fields in the vicinity of a silicon probe tip and a glass substrate. The results demonstrate that electric field enhancements of >15 relative to the incident fields can be achieved near a silicon tip, implying intensity enhancements of several orders of magnitude. This enhancement arises both from the antenna effect of the elongated probe and from a proximity effect when the probe is near the substrate surface and its image dipoles play a role.

Prolonged induction to delivery time in termination of pregnancy using 16, 16-dimethyl-PGE1-methyl ester (gemeprost) for fetuses with a neural tube defect or hydrocephalus.

A retrospective study is reported comparing the induction to delivery interval using gemeprost for termination of pregnancy, in the second trimester, in 3 groups of patients. It was observed that the mean induction to delivery interval was significantly longer in 75 pregnancies where there was a fetus with a neural tube defect and or hydrocephalus (31.7 hours) compared with 88 pregnancies with other fetal abnormalities (19.7 hours) and 84 pregnancies where there was an intrauterine death (11.3 hours). There was also an increase in the requirements for further intervention to obtain delivery in the group with a neural tube defect or hydrocephalus (n = 33) compared with where there was an intrauterine fetal death (n = 4) and other abnormality (n = 14). We believe these results should be considered when counselling patients who have requested termination of pregnancy for fetal abnormalities.

PIP: Investigated, in this retrospective study, was an observation of hospital staff that use of gemeprost in mid-trimester pregnancy terminations was associated with a longer induction-delivery interval when the fetus had been diagnosed with a neural tube defect or hydrocephalus. The records of a consecutive series of 247 women admitted to Western Suburbs Hospital (Waratah, New South Wales) in the second trimester for gemeprost-induced abortion were reviewed and women were divided into three groups according to indication: Group A (n = 24)--fetal death (not from neural tube defect or hydrocephalus) diagnosed by ultrasound; Group B (n = 88)--all chromosomal and structural abnormalities other than neural tube defect and hydrocephalus; and Group C (n = 75)--neural tube defect and/or hydrocephalus diagnosed by ultrasound. The mean induction interval was 11.3 hours in Group A, 19.7 hours in Group B, and 31.7 hours in Group C. The percentages of women with an induction to delivery interval equal to or exceeding 24 hours were 4.8%, 15.9%, and 43.4%, respectively. The proportion of women requiring further surgical intervention was 4% in Group A, 14% in Group B, and 33% in Group C. These findings should be considered when counseling women who request pregnancy termination for fetal abnormalities. It was hypothesized that fetuses with a neural tube defect or hydrocephalus have a deficiency of the hypothalamic-pituitary-adrenal axis, resulting in decreased corticotrophin-releasing hormone release and difficulty initiating parturition. Use of RU-486, in addition to gemeprost or extra-amniotic prostaglandin, may be indicated in such cases.

Absolute frequency stabilization of an injection-seeded optical parametric oscillator.

A method is described that provides absolute frequency stabilization and calibration of the signal and idler waves generated by an injection-seeded optical parametric oscillator (OPO). The method makes use of a He-Ne stabilized transfer cavity (TC) to control the frequencies of the cw sources used to seed both the pump laser and OPO cavity. The TC serves as a stable calibration source for the signal and idler waves by providing marker fringes as the seed laser is scanned. Additionally, an acoustic-optic modulator (AOM) is used to shift the OPO seed laser's frequency before locking it onto the TC. The sidebands of the AOM are tunable over more than one free spectral range of the TC, thereby permitting stabilization of the signal and idler waves at any frequency. A ±25-MHz residual error in the absolute frequency stabilities of the pump, signal, and idler waves is experimentally demonstrated, which is roughly 30% of the 160-MHz near-transform-limited linewidths of the signal and idler pulses.

Cytoskeletal organization in clusters of isolated polarized skate hepatocytes: structural and functional evidence for microtubule-dependent transcytosis.

Isolated hepatocytes from the marine vertebrate Raja erinacea (the little skate) retain their structural and functional integrity as clusters of cells formed around a single tubular bile canaliculus, and therefore can be used as a model of polarized hepatocytes in situ. In this study we used confocal and conventional epifluorescence microscopy in conjunction with fluorescent markers and immunocytochemistry to examine the structure and function of the cytoskeleton in these cells. Actin filaments in the hepatocyte clusters were found cortically and also concentrated in a pericanalicular array, while microtubules appeared to radiate away from a concentration near the apical membrane of the biliary pole towards the basolateral sinusoidal surfaces. Treatment of clusters with the microtubule disrupting agent, nocodazole, resulted in the microtubules depolymerizing from the basolateral surfaces towards the apical surface, indicating that the microtubules were oriented with their plus ends at the basolateral surface and their minus ends at the apical surface. Nocodazole was also found to disrupt the ability of clusters to transcytose a fluorescent bile salt derivative into their canalicular lumens. We detected cytoplasmic dynein in skate hepatocyte homogenates by Western blotting using an anti-dynein intermediate chain antibody, and immunofluorescent staining of intact hepatocytes revealed a punctate vesicular pattern. The polarized arrangement of microtubules, the presence of cytoplasmic dynein, and the inhibition of bile salt secretion by nocodozole are consistent with the microtubule cytoskeleton playing a fundamental role in the mediation of transcytosis, endocytosis, and bile excretory function in these hepatocytes. These polarized isolated skate hepatocytes represent an excellent experimental model for the in vitro study of hepatic transport, and allow for important comparative studies aimed at elucidating the evolutionarily conserved nature of various hepatocyte structures amongst the vertebrates.

Immunolocalization of kinesin in sea urchin coelomocytes. Association of kinesin with intracellular organelles.

We have recently used domain-specific monoclonal antibodies (mAbs) to immunofluorescently localize kinesin to vesicle-like structures in the cytoplasm of sea urchin coelomocytes. In order to characterize further these localization patterns we have examined the distribution of kinesin with respect to the arrangement of microtubules (MTs) and various organelles. In double-label experiments involving the immunofluorescent staining of kinesin (using a mixture of the mAbs SUK2, 4 and 5), MTs were labeled with an antiserum against sea urchin tubulin, the endoplasmic reticulum (ER) was labeled with an antiserum against a luminal calsequestrin-like protein, the Golgi apparatus was labeled with rhodamine-wheat germ agglutinin (WGA) or NBD-ceramide, mitochondria were labeled with rhodamine 123, endosomes were labeled with Texas Red-ovalbumin, and lysosomes were labeled with Lucifer yellow or acridine orange. Kinesin-labeled vesicle-like structures were found in the same regions of the cells as MTs and the ER, being widely distributed in motile cells, but restricted to the perinuclear regions of stationary cells. There also appeared to be a correlation between the distribution of endosomes and kinesin staining in a subpopulation of cells. The kinesin binding structures were found occasionally to align in linear arrays, consistent with the idea that kinesin may transport ER and endosomes along linear MT tracks. No clear correlations were observed between the kinesin staining and the distribution of mitochondria, the Golgi apparatus or lysosomes, suggesting that kinesin may specifically associate with only a subclass of organelles in coelomocytes.

Medical Communication Behavior System. An interactional analysis system for medical interactions.

The study assessed the psychometric properties of the Medical Communication Behavior System. This observation system records time spent by the physicians and patients on specific behaviors in the categories of informational, relational, and negative situation behaviors by using hand-held electronic devices. The study included observations of 101 genetic counseling sessions and also assessed the outcome measures of patient knowledge and satisfaction. In addition, 41 of the sessions were rated using the Roter Interactional Analysis System, and 20 additional control subjects completed the post-counseling information without being observed to examine the effects of recording the session. Results showed good interobserver reliability, and evidence of concurrent, construct, and predictive validity. No differences were found between the observed and unobserved groups of any of the outcome measures.