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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.

State-to-state reactive scattering of F+CH[sub 4]→HF(v,J)+CH[sub 3] is studied using crossed supersonic jets and high-resolution (Δνapprox. 0.0001 cm[sup -1]) IR laser direct absorption techniques. Rovibrational state-resolved HF column-integrated absorption profiles are obtained under single collision conditions and converted to populations via appropriate density-to-flux transformation. Nascent rovibrational distributions in each HF(v,J) state are reported. Summed over all product rotational levels, the nascent vibrational quantum state populations for HF(v) [(v=3) 0.106(3); (v=2) 0.667(14); (v=1) 0.189(27); (v=0) 0.038(78); 2σ error bars] are in agreement with previous flow cell studies by Setser, Heydtmann, and co-workers [Chem. Phys. 94, 109 (1985)]. At the rotational state level, however, the current studies indicate nascent distributions for HF(v,J) that are significantly hotter than previously reported, ostensibly due to reduced collisional relaxation effects under supersonic jet conditions. Final HF rotational states from F+CH[sub 4] are observed near the maximum energetically accessible J values in both the v=2 and v=3 vibrational manifolds, which provides experimental support for a bent F-H-C transition state structure. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nitrogen fluorescence induced by radiation can be used to detect the presence of radioactive contamination in the environment. Contamination quantification from the fluorescence signal requires: the source’s effective alpha spectrum; the specific radiation quantum fluorescence efficiency; optical attenuation length in air of the fluorescence signal; the absolute throughput and quantum efficiency of the optical instrumentation; calibration of the instrumentation; and radiation transport modeling of the “effective” array exposure rate given the alpha particle spectrum. Field testing conducted on optical instrumentation measured the nitrogen fluorescence yield generated by 241Am alpha emissions. Laboratory studies of 241Am via alpha spectrometry determined whether the presence of solids on source surfaces produced sufficient self-absorption to decrease fluorescence. Results from the laboratory studies provided correction to the effective alpha-source activity values in a model of the earlier optical-sensor field measurements, and determined the air fluorescence efficiency of alpha particles generated by the 241Am sources used in the field experiments. [ABSTRACT FROM AUTHOR]

• The dominant IR-active CH 3 I photolysis products are found to be CH 3 OH and HCHO. • An experimental photolysis rate for CH 3 I is determined. • Formaldehyde possesses a loss mechanism that contributes to the carbon deficit. • A preliminary kinetic model is proposed. Halogen-bearing compounds are known to photolyze under UV radiation; analysis of degradation products is of interest for both safety and environmental considerations. Time-resolved infrared spectroscopy was used in the laboratory to study the UV-photolysis of methyl iodide. Photolysis products methanol (CH 3 OH) and formaldehyde (HCHO) were clearly identified in a time-resolved manner. Preliminary kinetic models predict the formation of both CH 3 OH and HCHO. [ABSTRACT FROM AUTHOR]

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]