Showing papers by "Yutaka Matsumi published in 2000"

Effect of molecular bending on the photodissociation of OCS

Abstract: At 230 nm, the photodissociation of OCS via a hot band and a triplet state was investigated by selective probing of high rotational levels of product CO (J=45–67) with photofragment imaging spectroscopy: OCS(v=0)+hν(UV)→CO(X 1Σ+,J⩾65)+S(3P), OCS(v=1)+hν(UV) →CO(X 1Σ+,J∼65)+S(1D). Additional two-photon IR excitation of the UV photoprepared OCS with intense 1.06 μm laser pulses bleaches the UV processes listed above and induces a new excitation channel of OCS: OCS(v=0)+hν(UV)→OCS*, OCS*+2hν(IR)→CO(X 1Σ+,J∼74)+S(1S). The bending mode of OCS in the excited states plays a central role in the excitation and dissociation dynamics. Additionally, the alignment effect of OCS by nonresonant infrared laser pulse, which appears on the angular distribution of the photofragment, is discussed.

Control of photofragment velocity anisotropy by optical alignment of CH3I

Abstract: A molecule placed in an electric field can be aligned because of the anisotropy of its polarizability tensor. As an alternative to high static electric fields, the electric field of a pulsed laser can be used for alignment. The alignment can be demonstrated by measurement of the control of the anisotropy of photodissociated fragments generated by polarized light. Sakai et al. have recently reported such an experiment on aligned iodine molecules [J. Chem. Phys. 110, 10235 (1999)]. This paper reports an independent finding of the same phenomenon with CH3I. General equations are presented for the degree of alignment and its control of the photodissociation amplitude. The control parameter for a symmetric top or linear molecule is −(α−αzz)(E2/2kT)P2(cos χ), where α is the mean polarizability, αzz is the element of the polarizability tensor along the symmetry axis, and χ is the angle between the E vectors of the aligning and dissociating lasers. The fragment velocity anisotropy can be increased or decreased by...

Photodissociation of O3 around 309 nm

Abstract: Photodissociation reaction of O3 following ultraviolet photon excitation around the thermodynamic threshold of the dissociation channel of O(1D) + O2(a1Δg) at 309.44 nm has been studied under room-temperature and jet-cooled conditions. Both O(1D) and O(3P) photoproducts are detected by a technique of vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy. Photofragment excitation (PHOFEX) spectra for the O(1D) and O(3P) atoms are obtained by scanning the photolysis laser wavelength between 297 and 316 nm while monitoring VUV-LIF signal intensities at 115 and 130 nm for O(1D) and O(3P), respectively. From the behavior of the PHOFEX spectra for the O(3P) and O(1D) atoms around the threshold into O(1D) + O2(a1Δg), the existence of an exit barrier along the O−O2 dissociation coordinate in the photoexcited electronic state of O3 is suggested. Analysis of the line widths in the jet-cooled PHOFEX spectra of O(1D) and O(3P) suggests that the quasi-bound states below the barrier and above the thresho...

Relaxation Processes of Translationally Hot O(1D) by Collisions with O2

Abstract: The collisions of translationally hot O(1D) with O2 result in two processes, translational energy relaxation and electronic quenching to O(3P). These two processes were studied in a gas cell at room temperature using the vacuum ultraviolet laser-induced fluorescence technique. The initial hot O(1D) atoms were produced by the photodissociation of N2O at 193 nm, which have average translational energies of 18.1 kcal mol-1 in the laboratory frame. Time-resolved measurements of the Doppler profiles for the hot O(1D) atoms revealed the translational energy relaxation process, whereas the quenching process was investigated by measuring both the decrease of the O(1D) concentration and the increase of the product O(3P) concentration at various delay times after the photochemical formation of the hot O(1D) atoms. From the simulation employing an elastic hard-sphere collision model with a Monte Carlo method, the hard-sphere diameter for the translational energy relaxation process of hot O(1D) by collisions with O2 ...

Reaction kinetics of O(1D) with CF3CN

Abstract: The rate constant for removal of O(1D) by reaction with CF3CN has been measured to be (1.3 ± 0.2) × 10−10 cm3 molecule−1 s−1 at room temperature by a time-resolved laser induced fluorescence (LIF) technique. The quantum yield for the electronic quenching O(1D) to O(3P) has been also measured to be 0.14 ± 0.02. The O(1D) and O(3P) atoms were detected by LIF using a vacuum ultraviolet laser as a probe laser. CN(X2Σ+) and NCO(X2Π) products were also detected by LIF using ultraviolet and visible lasers, respectively. The CN(X) radical was observed as a primary product, while the NCO(X 2Π) radical was not observed as a primary product in the present reaction.