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We describe fully quantum, time-independent scattering calculations of the F+H2→HF+H reaction, concentrating on the HF product rotational distributions in v′=3. The calculations involved two new sets of ab initio potential energy surfaces, based on large basis set, multireference configuration-interaction calculations, which are further scaled to reproduce the experimental exoergicity of the reaction. In addition, the spin-orbit, Coriolis, and electrostatic couplings between the three quasidiabatic F+H2 electronic states are included. The calculated integral cross sections are compared with the results of molecular beam experiments. At low collision energies, a significant fraction of the reaction is due to Born–Oppenheimer forbidden, but energetically allowed reaction of F in its excited (2P1/2) spin-orbit state. As the collision energy increases, the Born–Oppenheimer allowed reaction of F in its ground (2P3/2) spin-orbit state rapidly dominates. Overall, the calculations agree reasonably well with the experiment, although there remains some disagreement with respect to the degree of rotational excitation of the HF(v′=3) products as well as with the energy dependence of the reactive cross sections at the lowest collision energies. [ABSTRACT FROM AUTHOR]

Exothermic reactive scattering of F atoms at the gas-liquid interface of a liquid hydrocarbon (squalane) surface has been studied under single collision conditions by shot noise limited high-resolution infrared absorption on the nascent HF(v,J) product. The nascent HF(v,J) vibrational distributions are inverted, indicating insufficient time for complete vibrational energy transfer into the surface liquid. The HF(v=2,J) rotational distributions are well fit with a two temperature Boltzmann analysis, with a near room temperature component (TTD≈290 K) and a second much hotter scattering component (THDS≈1040 K). These data provide quantum state level support for microscopic branching in the atom abstraction dynamics corresponding to escape of nascent HF from the liquid surface on time scales both slow and fast with respect to rotational relaxation. [ABSTRACT FROM AUTHOR]

Single collision reactive scattering dynamics of F+HD→HF(v,J) + D have been investigated exploiting high-resolution (Δv≈0.0001 cm[sup -1]) infrared laser absorption for quantum state resolved detection of nascent HF(v,J) product states. State resolved Doppler profiles are recorded for a series of HF rovibrational transitions and converted into state resolved fluxes via density-to-flux analysis, yielding cross-section data for relative formation of HF(v,J) at E[sub com]≈0.6(2), 1.0(3), 1.5(3), and 1.9(4) kcal/mol. State resolved HF(v,J) products at all but the lowest collision energy exhibit Boltzmann-type populations, characteristic of direct reactive scattering dynamics. At the lowest collision energy [E[sub com]≈0.6(2)kcal/mol], however, the HF(v=2,J) populations behave quite anomalously, exhibiting a nearly "flat" distribution out to J≈11 before dropping rapidly to zero at the energetic limit. These results provide strong experimental support for quantum transition state resonance dynamics near E[sub com]≈0.6kcal/mol corresponding classically to H atom chattering between the F and D atoms, and prove to be in remarkably quantitative agreement with theoretical wave packet predictions by Skodje et al. [J. Chem. Phys. 112, 4536 (2000)]. These fully quantum state resolved studies therefore nicely complement the recent crossed beam studies of Dong et al. [J. Chem. Phys. 113, 3633 (2000)], which confirm the presence of this resonance via angle resolved differential cross-section measurements. The observed quantum state distributions near threshold also indicate several rotational states in the HF(v=3) vibrational manifold energetically inaccessible to F(²P[sub 3/2]) reagent, but which are consistent with a minor (...5%) nonadiabatic contribution from spin-orbit excited F[sup *](²P[sub ½]). [ABSTRACT FROM AUTHOR]

Discusses the use of high-sensitivity direct infrared laser absorption methods to investigate quantum state-resolved reactive scattering dynamics in low-density crossed supersonic jets under single collision conditions. Nascent rotational state distributions and relative cross sections for reactive scattering.

A detailed examination of the ground and first excited singlet electronic states of HSiBr has been carried out through analysis of the 500–400 nm band system, using pulsed discharge jet and laser-induced fluorescence techniques. HSiBr and DSiBr have been produced by an electric discharge through SiHBr3 and SiDBr3 vapor in argon. Rotational analysis of the 000 bands yielded the structural parameters r0″(SiH)=1.518(1) Å, r0″(SiBr)=2.237(1) Å, θ0″=93.4(3)°, r0′(SiH)=1.497(10) Å, r0′(SiBr)=2.208(2) Å, and θ0′=116.4(7)°. Previous anomalies in the geometric parameters and vibrational frequencies have been resolved and the ground state bond lengths and vibrational frequencies are found to be comparable to those of SiH and SiBr. Harmonic force fields have been determined for the ground and excited states and the radiative lifetime of HSiBr has been measured to be 598±18 ns. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The spectroscopy and excited state dynamics of A 1B1 germylene (GeH2) have been investigated experimentally and theoretically. Jet-cooled laser-induced fluorescence spectra of GeH2 were obtained by subjecting germane (GeH4) to an electric discharge at the exit of a pulsed nozzle. The band origins of ten vibronic transitions were determined, giving values for the upper state fundamentals of ν1=783.0 cm-1 and ν2=1798.4 cm-1. Sufficient numbers of 000 band rovibronic transitions were observed to give the ground and excited state structures as r″=1.591(7) Å, θ″=91.2(8)° and r′=1.553(12) Å, θ′=123.4(19)°. Fluorescence lifetime measurements show that the 00,0 rotational levels decay radiatively; higher J rotational states in the 00 vibronic level decay much faster, due to a heterogeneous predissociation in the excited state. High quality ab initio studies are consistent with a model in which the lower vibronic levels of the A state predissociate through the a 3B1 state to produce Ge(3P)+H2(1Σ+g). The transition state for this process has been located and the barrier to dissociation is 15.2 kcal/mol above the A 1B1 state, so that tunneling through the barrier must occur. Above 4000 cm-1 of vibrational energy in the A state, a breaking off of fluorescence is observed as a second predissociation channel involving GeH2(A 1B1)→Ge(1D)+H2(1Σ+g) becomes accessible. This process is also found to have a barrier, in contrast to previous theoretical studies of SiH2, where the analogous dissociation was predicted to be barrierless. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The jet-cooled laser induced fluorescence excitation spectrum of the A 1A″–X 1A′ band system of HSiF has been observed with the chemical reaction jet technique. Vibrational analysis of the spectrum gave upper state fundamental vibrational frequencies of ν1=1547 cm-1, ν2=558 cm-1, and ν3=857 cm-1. Seven bands in the spectrum were recorded at high resolution and rotationally analyzed, providing excited state molecular constants. The upper state vibrational and rotational bending levels were fitted to a semirigid bender model to obtain the equilibrium geometry and the potential energy barrier to linearity. Due to correlations in the parameters, it was necessary to fix the bond angle at the ab initio value of 114.5°. The resulting fitted model yielded re(Si–F)=1.602 Å, re(Si–H)=1.548 Å with a potential energy barrier to linearity of 9130 cm-1. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the spectroscopic detection and characterization of iodogermylene. Use of pulsed discharge and laser-induced fluorescence techniques; Analysis of the partially resolved rotational structure of the energy bands; Account on the fluorescence lifetime of the monoiodogermylene.

Examines the electronic spectrum of monoiodosilylene (HSil). Details on the excited state vibrational frequencies of HSil; Use of the pulsed discharge technique; Revision of the literature value of v'[sub 1].

Examines the jet-cooled electronic spectra of monochlorogermylene (HGeCl) and monobromogermylene (HGeBr) in semiconductor devices. Details on the formation of germylenes; Role of chemiluminescence dispersion in electronic emission spectra; Information on Laser-induced fluorescence spectra.

Studies the jet-cooled spectrum of silylidene, a simple form of unsaturated silylene. Characteristics of band consisting the electronic transition; Excited state decay dynamics; Rotational levels specific intensity anomalies; Beat patterns due to coupling with high vibrational levels of the ground state.

Examines the ground and first excited singlet states of monochlorosilylene complexes in various levels of electronic spectra. Use of pulsed discharge jet and laser induced fluorescence techniques; Production of the complex by an electric discharge; Band rotational constants of four isotopomers; Levels of harmonic force fields.

Describes the pulsed discharge jet spectroscopy of DSiF and the equilibrium molecular structure of monofluorosilylene. Upper state harmonic vibrational frequencies of the DsiF spectrum; Excited state equilibrium structure; Average structures for ground and excited states; Rotational analysis of vibronic bands involving upper state fundamentals of HsiF and DsiF.

Heavy atom analogs, silylidene, H2C=Si and germylidene, H2C=Ge are not well known, although theoretical studies show that silylidene is the global minimum on the H2CSi potential surface. The production of jet-cooled H2C=Si and H2C=GE was undertaken, by striking an electric discharge in tetramethylsilane (TMS) or tetramethylgermane (TMG) vapour. Silyidene showed evidence of intensity anomalies in the LIF spectra.

A temperature dependent kinetic investigation of the catalytic HOx ozone cycle, OH + O3 - HO2 + O2 and HO2 + O3 - OH + 2 O2, based on time-resolved, Dopper limited direct absorption spectroscopy of OH with a single mode high-resolution infrared laser, is presented.