H. Ohoyama

Initial distribution of vibration of the OH radicals produced in the H + O3 → OH(X2Π1/2,3/2) + O2 reaction. Chemiluminescence by a crossed beam technique

Abstract The chemiluminescence in the H + O 3 → OH(X 2 Π 1/2,3/2 ) + O 2 reaction was observed using a crossed beam technique. The initial population of the OH radicals in the vibrational state v (4 ⩽ v ⩽ 9) were found to be N (9) = 1.0, N (8) = 0.95 ± 0.1, N (7) = 0.9 ± 0.2, N (6) = 0.2 ± 0.1 and N (5) = N (4) = 0.2 ± 0.2. The total cross section of the formation of OH(4 ⩽ v ⩽ 9) was estimated to be of the order of 10 −2 nm 2 . No chemiluminescence was observed in the reaction D + O 3 → OD(X 2 Π 1/2,3/2 ) + O 2 under the present experimental conditions.

Evidence for steric effect in methyl chloride ionization by metastable argon atoms

Abstract The orientation dependence of methyl chloride ionization by collision with metastable argon atoms at an average collision energy of 0.09 eV has been investigated using an electric hexapole field selector followed by an orienting field. The steric opacity function of the process has been determined. The highest reactivity has been found for approaches of the metastable atom towards the Cl-end of the molecule, while the lowest corresponds to the opposite approaches, close to the CH 3 -end. The stereo-selectivity is discussed in terms of spatial distribution of the highest occupied molecular orbital of CH 3 Cl, mainly localized on the chlorine atom.

Experimental determination of the dipole moment of HCl dimer using an electrostatic hexapole field

Abstract HCl dimers were prepared in a pulsed supersonic beam of neat HCl. The dimers were focused in an electrostatic hexapole field. Using computer simulation, the focusing curve could be fit, assuming contributions from both first and second order Stark effects. The dipole moment, based on simulation, was found to be 1.5 ± 0.1 D. The ability to observe an effective dipole moment in a system where the donor-acceptor tunneling is fast is surprising. It may indicate that the understanding of the interaction of floppy systems with hexapole field is not complete.

Formation of an intense pulsed beam of CH3Cl in the ‖111≳ state using a 2‐m electrostatic hexapole field

An intense pulsed beam of CH3Cl in the ‖111≳ state without velocity selection was focused using a 2‐m electrostatic hexapole field. The beam intensity was estimated to be ∼1×1013 molecules pulse−1, which is much greater than the similar beams in the earlier study of Gandhi et al. by at least two orders of magnitude. The beam had a 3‐ms pulse width and was focused with an angular divergence of 0.7 mrad. The improvements in beam intensity and in the divergence of the beam can be mainly ascribable to the efficient pumping of the hexapole field through the cylindrical electrodes, which enables us to employ the helium seeding to have the fast stream velocity, the narrow distribution of velocity, and the aerodynamic effects. Those factors altogether made the velocity selection of the beam unnecessary.

Orientation-dependent CF3 emission observed in the Ar(3P) + CF3H → CF*3 (1E′, 2A″2) + H + Ar reaction

Abstract The orientation-dependent CF 3 emission in the visible region observed in the Ar( 3 P) + CF 3 H reaction was investigated. The Legendre polynomial and Engel-Levine function expansions were applied to obtain an orientational opacity function, in which the lowest six terms of the Legendre series were found to be important to reproduce the observed orientational dependence. In both cases, these opacity functions reveal three reactive sites. The most favorable one is the attack of the Ar( 3 P) atom at the CF 3 group in the collinear approach and the second one correlates with the direct approach to the F atom. The least favorable site is centered at around 140° in the region of H atom attack. There is a cone of small reactivity in the collinear direction at the H-end attack. Although the exchange interaction cannot completely explain the relative reactivity at each reaction site, the shape of the opacity function was attributed to the exchange interaction between the 6a 1 molecular orbital of CF 3 H and the 3p empty core orbital of Ar( 3 P).

Orientation dependence of chemiluminescence spectra of CF3 formed in the reaction of oriented CF3H with Ar(3P)

Chemiluminescence of the CF*3 radical formed in the reaction of Ar(3P) with the oriented CF3H was taken at five different wavelengths in the range from 500 to 700 nm for two reactant orientations with a reference orientation. A remarkable alignment dependence of the emission spectra was observed. Analysis of the wavelength dependence of the CF3 chemiluminescence revealed the existence of three reactive sites due to two reaction mechanisms. One is preferable at the side-on orientation and the second is both at the CF3 end and H end orientations.

Metal–ligand interaction of Ti–C6H6 complex size-selected by a 2-m long electrostatic hexapole field

Abstract Supersonic beam of size-selected Ti–C6H6 metal–ligand binary complex was generated by a laser evaporation method followed by the size selection with 2-m long electrostatic hexapole field. The dependence of the beam intensity upon the hexapole field strength was measured in order to determine permanent dipole moment and complex symmetry. We find that the structure of Ti–C6H6 complex has nearly C6v symmetry and its electric dipole moment is 2.4±0.3 D. The calculation with use of density functional theory substantiated its optimized structure as C6v symmetric in accordance with the experimental result. The calculation also suggests that charge transfer interaction between Ti atom and C6H6 plays a central role to stabilize the complex.

Formation and characterization of an SH(2II32,12) radical beam produced by the F + H2S reaction using a sextupole electric field

Abstract An unstable free radical beam of SH was produced by the reaction of fluorine atoms with H2S and effused from a Teflon nozzle. The beam was focused using sextupole electric fields. Monte Carlo trajectory simulations showed 300 ± 50 K as the rotational temperature for the chemically produced SH, so that an oriented SH beam with (cos θ ) = − 0.28 could be available in the presence of an intense electric field. The beam intensity of the focused SH is estimated to be about 1011 molecule sr−1 s−1.

Focusing of DCl and HCl dimers by an electrostatic hexapole field: The role of the tunneling motion

The focusing of HCl and DCl dimers was observed using a 2-m-long electrostatic hexapole field. The results indicate the existence of two types of species. The first is the homodimers, either the H35Cl–H35Cl or the D35Cl–D35Cl, for which the data indicate a fast tunneling motion. The second is the heterodimers, H35Cl–H37Cl or D35Cl–D37Cl, that do not show evidence for significant tunneling motion on the time scale of the experiment. In the case of HCl dimers, even at relatively high fields, only one species could be focused, the heterodimer. The electric dipole moments for both (DCl)2 isotopomers were determined to be 1.5±0.2 D, which is the same value as observed for (HCl)2.

Observation of orientation-dependent CF3 chemiluminescence in the reaction of Ar(3P0,2) with oriented CF3H

Abstract Orientation-dependent CF 3 chemiluminescence from 430 to 930 nm was observed for the first time in the reaction of pulsed supersonic molecular beams of metastable argon atoms and oriented CF 3 H molecules. The “sideways configuration” of CF 3 H as well as the “F-end configuration” was found to be more reactive than the “H-end configuration”. The Legendre expansion technique of Stolte et al. was applied up to the fourth term. A dissimilar dependence of reactivity on molecular orientation for the UV emission of CF 3 was also indicated from the present experiment.