Shigeru Tsunashima

Reactions of N(2 2D) and N(2 2P) with H2 and D2

Rate constants for the reactions N(2 2D)+ H2(D2) and N(2 2P)+ H2(D2) have been measured by employing a pulse radiolysis–resonance absorption technique at temperatures between 213 and 300 K. The rate constants were expressed by the following Arrhenius equations: kN(2D)+H2= 4.6 × 10–11 exp(–8.8 × 102/T), kN(2D)+D2= 3.9 × 10–11 exp(–9.7 × 102/T), kN(2P)+H2= 3.5 × 10–13 exp(–9.6 × 102/T) and kN(2P)+D2= 1.9 × 10–13 exp(–9.2 × 102/T), in units of cm3 s–1. The results for N(2P) suggest that the main exit channels are not chemical reactions to produce NH (ND) radicals. The Arrhenius parameters for N(2D)+ H2(D2) are compared with the results of transition-state theoretical calculations as well as those of quasiclassical trajectory calculations on the basis of extended LEPS potential-energy surfaces.

REACTIONS OF C(1D) WITH H2, HD AND D2 : KINETIC ISOTOPE EFFECT AND THE CD/CH BRANCHING RATIO

Abstract Electronically excited carbon atom C( 1 D ) was produced by the 308 nm two-photon dissociation of C3O2. CH and CD radicals produced by the reactions of C( 1 D )+H2, HD and D2 were probed by laser-induced fluorescence. The nascent rotational state distributions of CH(v=0) and CD(v=0) were measured under single collision conditions. The distributions measured in the present study were close to those obtained in the previous studies using the 157 nm photodissociation. The rate constants at the room temperature were measured to be (2.0±0.6)×10−10, (1.7±0.4)×10−10 and (1.4±0.3)×10−10 cm3 molecule−1 s−1 for the reactions with H2, HD and D2, respectively. The CD/CH branching ratio in the C( 1 D )+HD reaction was determined to be 1.6±0.1. The preference of the CD production suggests that this reaction proceeds mainly via the HCD intermediate complex.

STUDIES OF THE N(2D) + H2 REACTION ON REVISED POTENTIAL ENERGY SURFACES

Abstract The dynamics of the N( 2 D) + H 2 reaction has been studied by quasiclassical trajectory methods and compared with the experimental results. Several potential energy surfaces were used. The product vibrational distribution was affected by the modification of the entrance channel barrier. Neither the product vibrational nor rotational distribution was affected by the modification of the deep well, which corresponds to NH 2 . The product rotational distribution was found to be mainly affected by the topology of potential energy surface at the exit channel region.

Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes

The 193 and 157 nm photodissociations of three isomers of dichloroethylene (DCE) and trichloroethylene (TCE) were investigated using a technique of photofragmentation translational spectroscopy. The photofragmentation mechanisms were constructed by analyzing the time-of-flight spectra of C2H2+, Cl+, HCl+, C2HCl+, and C2Cl2+ produced by electron impact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C–Cl bond rupture were important for all the compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C–Cl bond rupture was important even at 193 nm. In the 157 nm photodissociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C–Cl bond rupture occurred for trans-DCE. This result suggests that the 157 nm photodissociation of trans-DCE proceeds via the direct photodissociation following the photoexcitation to the repulsive 1nσ* state. A minor...

The absolute cross sections for quenching of cadmium 53P1 and 53P0 atoms by methane, nitrogen and isotopic hydrogens

Abstract A phase-shift method was used to determine the absolute cross sections for the quenching of Cd( 3 P 1 ) and Cd( 3 P 0 ). The phase difference between the excitation at 326.1 nm and the fluorescence from Cd( 3 P 1 ) atoms was measured as a function of the pressure of the quenching gases. The rate constants for the intramultiplet mixing were also determined for methane, nitrogen and isotopic hydrogens. Isotopic hydrogens were found to produce Cd( 3 P 0 ) from Cd( 3 P 1 ) very efficiently.

Nascent internal state distributions of ZnH(X 2Σ+) produced in the reactions of Zn(4 1P1) with some alkane hydrocarbons

The reactions of Zn(4 1P1) with CH4, C2H6, C3H8, and C(CH3)4 were studied by employing a laser pump‐and‐probe technique. The nascent rotational and vibrational state distributions of ZnH(X 2Σ+) were determined. These distributions were compared with those predicted by statistical models. The distributions for C(CH3)4 resembled to the statistical ones, while those for simple alkanes such as CH4 were a little hotter than the statistical ones. These results suggest that the reaction proceeds via a relatively long‐lived insertive complex. There was no great difference in the production yields of ZnH, although that for CH4 was the largest.

The infinite‐order‐sudden‐approximation calculations of reactive cross sections and product angular distributions for the F+H2 reaction and its isotopic variants on a modified London–Eyring–Polanyi–Sato potential energy surface

The reactive cross sections and product angular distributions for the F+H2,F+D2 and F+HD reactions have been calculated using the infinite‐order‐sudden approximation on a modified London–Eyring–Polanyi–Sato potential energy surface which has a nonlinear saddle point. This surface was constructed previously so as to reproduce the experimentally obtained product angular distributions by the quasiclassical trajectory calculations. The calculated branching ratios of different vibrational states of products, HF(v’) and DF(v’) from above three reactions, were all in qualitative agreement with those experimentally obtained; however, the product angular distributions calculated were not better than those calculated by the quasiclassical trajectory method. These results are compared with those calculated on different potential surfaces which predict collinear transition states.

QUASICLASSICAL TRAJECTORY STUDIES OF N(2D) + H2 REACTION ON A FITTED AB INITIO POTENTIAL-ENERGY SURFACE

The dynamics of the N(2D)+ H2 reaction has been investigated by quasiclassical trajectory calculations on a new potential-energy surface which was constructed on the basis of ab initio results. The calculated vibrational distribution for the NH product agreed well with that measured by Dodd et al.(J. A. Dodd, S. J. Lipson, D. J. Flanagan and W. A. M. Blumberg, J. Chem. Phys., 1991, 94, 4301). The thermal rate constants and isotope effects calculated on this surface were in moderate agreement with those recently determined. At a low collision energy, the N atom mainly approaches the H2 molecule collinearly and an NH radical is produced via the deep well corresponding to a stable NH2. At a high collision energy, a perpendicular approach is found to be important in addition to the collinear approach.

The photodissociation dynamics of dichloroethenes at 214 and 220 nm

The nascent rotational distributions of HCl (v=0, 1, and 2) generated in the photodissociation of three isomers of dichloroethenes (DCE) at 214 and 220 nm were measured under molecular beam conditions. HCl molecules were probed by a (2+1) resonantly enhanced multiphoton ionization technique combined with time‐of‐flight mass spectrometry. The rotational distributions of vibrationally excited HCl (v=1 and 2) molecules were Boltzmann‐type, while those of HCl (v=0) could not be represented by a Boltzmann distribution and consisted of two components. These results suggest that there are more than two processes in the photodissociation of DCE. Cl(2P3/2) and Cl*(2P1/2) could also be detected when DCE were photodissociated. The branching ratios of Cl*(2P1/2) to Cl(2P3/2) obtained in the present work were much larger than those obtained at 193 nm.

Intersystem crossing and intramultiplet mixing of excited Zn atoms by Xe

The intersystem crossing of Zn(4 1P1) and the intramultiplet mixing of Zn(4 3PJ) by Xe were examined by using pulsed laser techniques. The following thermally averaged cross sections were obtained: Zn(4 1P1)+Xe→Zn(4 3P2)+Xe: 3.4, Zn(4 1P1)+Xe→Zn(4 3P1)+Xe: 0.4, Zn(4 1P1)+Xe→Zn(4 3P0)+Xe: <0.01, Zn(4 3P1)+Xe→Zn(4 3P2)+Xe: 12.0×10−3, Zn(4 3P1)+Xe→Zn(4 3P0)+Xe: 6.3×10−3, in units of 10−16 cm2. These experimental results could well be reproduced by quantum close‐coupling calculations by assuming suitable potential energy curves. The intersystem crossing by He was found to be inefficient.