TUNABLE VACUUM ULTRAVIOLET PHOFEX SPECTROSCOPY OF OCS

Author Institution: Department of Pure and Applied Sciences, College of Arts and Sciences, The University of TokyoThe photofragment excitation (PHOFEX) spectrum of jet-cooled OCS has been measured in the vacuum ultraviolet (VUV) region between 140-160 nm. The electronically excited S($^{1}S$) photoproduct, produced by tunable VUV laser photolysis, was detected by laser induced fluorescence via the $^{3}D_{1}{^{\circ}} - ^{1}S$ transition. The observed PHOFEX spectrum is better resolved than previous room-temperature and jet-cooled absorption spectra, and new features are observed. The dynamics of the photodissociation will be discussed using the measured PHOFEX spectrum, as well as the $S(^{1}S)$ Doppler profiles

VIBRATIONAL SPECTROSCOPY OF A TRANSIENT SPECIES THROUGH TIME-RESOLVED FOURIER TRANS-FORM IR EMISSION SPECTROSCOPY: THE VINYL RADICAL

Author Institution: Department of Chemistry, University of Pennsylvania; Department of Chemistry, American University; Department of Chemistry, Howard University; Department of Chemistry, University of PennsylvaniaAn approach for detecting the vibrational spectrum of transient species is demonstrated on the vinyl radical. Photodissociation of carefully chosen precursors at a selected photolysis wavelength produce highly vibrationally excited radicals. IR emission from these radicals is then measured by time-resolved Fourier Transform Spectroscopy with nanosecond time resolution. This technique has the advantage of probing a wide frequency range of the IR spectrum in a single experiment. Using this method, all 9 vibrational bands of the vinyl radical, generated from 4 different precursors, are obtained for the first time. The cyanovinyl radical has also been studied and previously unknown vibrational assignments were made

THE VISIBLE SPECTRUM OF THE VINYL RADICAL MEASURED WIHT CAVITY RING-DOWN LASER ABSORPTION SPECTROSCOPY

Author Institution: Department of Chemistry, American University; Combustion Research Facility, Sandia National LaboratoryThe vinyl radical $(C_{2}H_{3}) \tilde{A}^{2}A^{\prime \prime} \leftarrow \tilde{X}^{2}A^{\prime}$ absorption spectrum has been measured in a room temperature gas cell over the wavelength range 415-530 nm at 0.008 nm resolution using the technique of cavity ring-down laser absorption spectroscopy. The present measurement is 200 times higher resolution than the previously recorded absorption spectrum in this wavelength range. There is considerable lifetime broadening of the observed rotational structure, corresponding to an excited state lifetime of 50 ps. An assignment of the observed vibrational structure will be presented as will preliminary results from jet-cooled spectra

SPECTROSCOPY OF THE RYDBERG STATES OF XeKr IN THE 68000CM−168 000 CM^{-1} REGION

Author Institution: Department of Pure and Applied Sciences, The University of Tokyo; Department of Chemistry, Massachusetts Institute of TechnologyThe laser induced fluorescence spectrum of XeKr, prepared in a free-jet expansion, was obtained near the $Xe 6s[3/2]^{\circ} (J=1) <- {^{J}}S_{0}$ transition $(68045.66 cm^{-1})$. Transitions to three electronic states were identified within a $300 cm^{-1}$ range. Complex vibrational structure in the discrete spectra is attributed to an avoided crossing between two $\Omega = 1$ states. Bound-free transitions were also observed when exciting to repulsive states that produce an excited $Xe 6s[3/2]^{\circ} (J=1)$ atom. Spectroscopic constants and approximate potentials will be presented

Pressure and Temperature Dependence of the Reaction of Vinyl Radical with Alkenes III: Measured Rates and Predicted Product Distributions for Vinyl + Butene

This work reports experimental and theoretical first-order rate constants for the reaction of vinyl radical with C4H8 alkenes: 1-butene, 2-butene, and iso-butene. The experiments are performed over a temperature range of 300 K to 700 K at 100 Torr. Vinyl radicals (H[subscript 2]C=CH) were generated by laser photolysis of vinyl iodide (C[subscript 2]H[subscript ]3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals at 423.2 and 475 nm. Weighted Arrhenius fits to the experimental rate coefficients for 1-butene (k[subscript 1]), 2-butene (k[subscript 2]), and iso-butene (k[subscript 3]) yield k[subscript 1] = (1.3±0.3)× 10[superscript -12] cm[superscript 3] molecules[superscript -1] s[superscript -1] exp[-(2200 ± 120) K/T]; k2 = (1.7±0.3)× 10[superscript -12] cm[superscript 3] molecules[superscript -1] s[superscript -1] exp[-(2610 ± 120) K/T]; k[superscript 3] = (1.0±0.1)× 10[superscript -12] cm[superscript 3] molecules[superscript -1] s[superscript -1] exp[-(2130 ± 50) K/T], respectively. C6H11 potential energy surfaces (PES) for each system were calculated using the G3 method. RRKM/ME simulations were performed for each system to predict pressure dependent rate coefficients and branching fractions for the major channels. A generic rate rule for vinyl addition to various alkenes is recommended; a similar rate rule for the abstraction of H atoms by vinyl from alkenes is also provided. Some of the vinyl addition reactions exhibit anomalous Evans-Polanyi plots, similar to those reported for previous methyl addition reactions.United States. Dept. of Energy (contract DE-FG02-98ER14914)United States. Dept. of Energy. Office of Basic Energy SciencesUnited States. Dept. of Energy. Chemical Sciences, Geosciences, and Energy Biosciences Divisio