Showing papers by "Yutaka Matsumi published in 1994"

Velocity relaxation of hot O(1D) atoms by collisions with rare gases, N2, and O2

Abstract: Speed and angular relaxation processes induced by collisions with He, Ar, Ne, Xe, N2, and O2 for the velocity of superthermal O(1D) photofragments have been studied by measuring the Doppler profiles of O(1D) as a function of the time delay between photolysis and probe laser pulses. The nascent O(1D) atoms, generated in the photodissociation of O2 by linearly polarized light at 157 nm, have a narrow kinetic energy distribution, centered at 9.8 kcal/mol and a large angular anisotropy. The O(1D) atoms are probed with a tunable vacuum‐ultraviolet laser at approximately 115.2 nm. The time evolution of the speed distribution is extracted from the Doppler profiles for each bath gas. The anisotropy parameter distribution as a function of the speed at each time delay is also obtained. The distributions obtained indicate that (a) a collision with He reduces the speed of the O(1D) atom efficiently but only changes slightly the direction of its velocity and (b) a collision with Ne or Ar reduces its speed efficiently ...

Fine structure branching ratios and translational energies of O(3Pj) atoms produced from collision induced intersystem crossing of O(1D) atoms

Abstract: Collision induced intersystem crossing of O(2p 1D) to O(2p 3Pj) j=0,1,2 was studied by vacuum‐ultraviolet laser induced fluorescence The nascent j‐branching ratios of O(3Pj) produced from collision of O(1D) with Xe, Kr, N2, CO2, and CF3H at the collision energy of 156, 147, 114, 130, and 144 kcal/mol are [O(3P0)]/[O(3P1)]/[O(3P2)]=(028±004)/(058±005)/1, (033±005)/(045±007)/1, (023±005)/(035±005)/1, (014±005)/(041±005)/1, and (020±005)/(045±005)/1, respectively The j‐branching ratios are discussed in terms of potential curve crossing between singlet and triplet surfaces and nonadiabatic nature of the potential surfaces Doppler profiles of the product O(3Pj) atoms were measured as a function of time delay between pump and probe laser pulses By calculating the kinetic energy from the Doppler profiles, electronic energy transfer efficiencies to the internal energy of N2, CO, CO2, and CF3H are obtained to be (30±7), (31±7), (49±3), and (52±5)%, respectively

Dynamics of the reaction s(1d) + hd, h2, and d2: isotopic branching ratios and translational energy release

Abstract: Doppler profiles of H and D atoms from the reaction S(1D) with HD and a 1:1 mixture of H2 and D2 have been measured by a laser-induced fluorescence technique with a vacuum ultraviolet laser. An isotopic channel branching ratio of φ (SD + H)/φ (SH + D) is measured to be 0.9 ± 0.1 in the reaction of S(1D) + HD at average collision energy Ecoll = 1.2 kcal/mol. In S(1D) + HD, D2, and H2, the translational energies released are almost the same, 4.6 ± 0.5 kcal/mol for H and D production channels. The measured branching ratio and translational energy release suggest that the reaction proceeds via a long-lived complex formed by insertion.

Collisional relaxation of translational energy and fine‐structure levels of the O(3Pj) atom created in the photodissociation of SO2 at 193 nm

Abstract: Collision‐induced energy transfer and intramultiplet relaxation processes of O(2p4 3Pj) j=0, 1, and 2 have been studied, using a vacuum‐ultraviolet laser‐induced fluorescence technique. The O(3Pj) atoms are produced from the photodissociation of SO2 at 193 nm. Doppler profiles of the O(3P2) atoms have been measured as a function of time delay between pump and probe laser pulses. The translational energy and j‐level population of the O(3Pj) atoms are thermalized at 300 K after a number of collisions with either He, Kr, Xe, N2, or CO2. A Monte Carlo calculation using the hard‐sphere collision model provides the cross sections for relaxation of the translational energy; 21±3 A2 for He, 25±3 A2 for Kr, and 25±5 A2 for Xe. Assuming the principle of detailed balancing among the j levels, the cross sections for the collision‐induced intramultiplet transition over the collision energy range 1–6 kcal mol−1 are obtained from the time evolution of the j‐level populations: cross sections for the j=2→1 transition are ...

O(3Pj) atom formation from photodissociation of ozone in the visible and ultraviolet region

Abstract: The photodissociation of ozone at 266, 308, and 532 nm has been studied for probing O(3Pj) atomic photofragments by a vacuum ultraviolet laser-induced fluorescence method. Angular distributions and...

Isotopic Branching Ratios and Translational Energy Release of H and D Atoms in the Reaction of O(1D) with CH3OD and CD3OH

Abstract: H and D atoms produced from the reaction of O( 1 D) with isotopically substituted methanols have been measured by laser-induced fluorescence at 121.6 nm. At a collision energy of 7.3 kcal/mol, the product isotope ratios [H]/[D] are 0.26±0.03 and 7.1±0.8 for the reaction of O( 1 D) with CH 3 OD and CD 3 OH, respectively. Measured isotopic branching ratios are discussed in terms of the site-selective attack of O( 1 D) atoms to the C-H bond followed by preferential breaking of the new O-H bond

Laser‐induced fluorescence detection of ClO radicals at 167–180 nm

Abstract: ClO radicals are detected by a laser‐induced fluorescence technique, using the C 2Σ–X 2Π transition with a tunable vacuum ultraviolet laser system. Predissociation in the C 2Σ state is discussed in terms of the fluorescence lifetime and excitation spectra. The vibrational distribution of ClO produced by the reaction between O1D and HCl is measured.