Showing papers by "Yutaka Matsumi published in 1991"

Fine structure branching ratios and Doppler spectroscopy of chlorine atoms from the photodissociation of alkyl chlorides and chlorofluoromethanes at 157 and 193 nm

Abstract: Alkyl chlorides (R=CH3, C2H5, C3H7, and C4H9), chloromethanes (CHnCl4−n), and chlorofluoromethanes (CFnCl4–n) are photodissociated at 157 and 193 nm. The chlorine atom photofragments are detected by a resonance enhanced multiphoton ionization technique. The branching ratios of the Cl photofragments [Cl*(3p2P1/2)]/[Cl(3p2P3/2)] are almost identical (0.23±0.03) for alkyl monochlorides at 157 and 193 nm and for CH2Cl2 and CHCl3 at 157 nm, while the ratios are rather small (0.10±0.02) for CH2Cl2 and CHCl3 at 193 nm. No discernible isotope effects on the branching ratios were observed when D atoms were substituted for H atoms in chloromethanes. For CCl4, CF3Cl, CF2Cl2, CFCl3 at 157 and 193 nm, the ratios are small (<0.05) irrespective of the number of Cl atoms in the parent molecules. The Doppler profiles of the chlorine photofragments have been obtained and it is found that (a) CF3Cl undergoes a perpendicular optical transition at 157 nm and (b) for halomethanes containing more than two Cl atoms, the Cl photo...

The Doppler spectra of O(1D) from the photodissociation of O2, NO2, and N2O

Abstract: The Doppler profiles of the O(1D) products from the photodissociation of O2 at 157.6 nm and NO2 and N2O at 205.47 nm are detected by a resonance enhanced multiphoton ionization technique. The translation energy and angular distributions are deduced for the O(1D) atoms. Present results indicate that (a) O2 (B 3Σ−u) has a short dissociative lifetime when irradiated at 157.6 nm, (b) NO(2Π) photofragment from NO2 at 205.47 nm is mostly vibrationally excited, and (c) most of the available energy is released as kinetic energy when N2O is photodissociated at 205.47 nm.

Doppler profiles and fine‐structure branching ratios of O(3Pj) from photodissociation of carbon dioxide at 157 nm

Abstract: The O(2p 3Pj) (j=2, 1, and 0) fragments produced in the 157 nm photodissociation of CO2 were detected by resonance‐enhanced multiphoton ionization in a molecular beam. The Doppler profiles and fine‐structure branching ratios were measured for the oxygen‐atom photofragment in the 3Pj states. The Doppler profiles were analyzed to give an anisotropy parameter of β=2.0±0.2 and an internal energy equivalent to 3.9±0.3 vibrational quanta of CO. The fine‐structure populations were found to be 0.70±0.05, 0.16±0.03, and 0.14±0.03 (with error bars of ±σ) for j=2, 1, and 0, respectively. A mechanism is proposed in which complex on the 1B2 surface undergoes intersystem crossing to the 3B2 surface. A phase‐space model with a constraint on the impact parameter is shown to be consistent with the observed energy release. The nonstatistical fine‐structure population could be caused by long‐range interactions on the triplet surface. In a bulb experiment, O(3P) was produced by quenching of O(1D). The fine‐structure populati...

Doppler spectroscopy of hydrogen atoms from the photodissociation of saturated hydrocarbons and methyl halides at 157 nm

Abstract: Hydrocarbons (CnH2n+2, n=3, 4, and 6) and methyl halides (CH3X, X=Cl, Br, I) are photodissociated at 157 nm. The hydrogen atom photofragments are detected by a resonance‐enhanced multiphoton ionization technique. The Doppler profiles of the hydrogen atoms from hydrocarbons are well represented by a Gaussian profile, while those from methyl halides by a mixture of a Gaussian and a non‐Gaussian profiles. These Doppler profiles are interpreted assuming that (a) hot ethyl photofragments from hydrocarbons result in the formation of hydrogen atoms and (b) methyl halides undergo both direct and indirect photolytic scissions of the C—H bonds at 157 nm.

Fine structure branching ratios and Doppler spectra of O(3Pj) produced by the reaction of H+O2→OH+O

Abstract: O(2p3Pj) atoms produced from the reaction between H(1s2S) and O2(X3Σ−g) at collision energies (Ecoll) of 2.5 and 2.1 eV are detected by a resonance enhanced multiphoton ionization technique. From the Doppler profile measurements of O(3Pj), the average kinetic energy released to the products is estimated. The results suggest that the average fraction of the kinetic energy disposal at Ecoll =2.1 eV is larger than that at Ecoll =2.5 eV. The obtained branching ratios of O(3Pj) j=2, 1, and 0 at Ecoll =2.5 eV are (0.70±0.02), (0.21±0.02), and (0.09±0.02), and those at Ecoll =2.1 eV are (0.63±0.02), (0.25±0.04), and (0.12±0.02), respectively, with error bars of ±σ. The results suggest that the nonadiabatic couplings at the last stage of the reaction are important for the determination of the ratios.

Photodissociation of oxygen molecules at 226 nm in the Herzberg I system

Abstract: Doppler profiles of O(2p 3Pj) (j=2,1,0) produced from the photodissociation of O2 in the Herzberg I system (A3Σ+u←X3Σ−g) at 226 nm are measured with a resonance‐enhanced multiphoton ionization technique. The anisotropy parameter for the angular distribution of the photofragments is found to be 1.6±0.4, in quantitative agreement with theory and indicating that the Herzberg I system borrows most of its intensity from a parallel band. The branching ratios to the j levels of O(2p 3Pj) (j=2,1,0) are found to be (2.5±0.3):1:(0.26±0.03) and are compared with the values expected for the limits of adiabatic and diabatic dissociation.

Pyrolytic and photolytic dissociation of trimethylgallium on Si and Au substrates

Abstract: Pyrolytic dissociation of trimethylgallium (TMGa) on Si, Au, and Al substrates was studied at various temperatures from 80 to 670 K by x‐ray photoelectron spectroscopy of Ga (3d) and C (1s). The intensity and band profile of carbon and gallium signals from TMGa adsorbed on the substrates were measured. The results indicate that TMGa on Si (111) dissociates into Ga and CH3 on the substrate even at 200 K and CH3 further dissociates into C, CH, and CH2 at higher temperatures. Most carbon and gallium species remain on the Si substrate. Carbon species leave the Au and Al substrate but Ga remains on the surface. The pyrolysis of TMGa on GaAs (100), Si (111), and Si (100) substrates is compared and the mechanism of carbon incorporation in photolysis and pyrolysis is discussed. Photodissociation of a monolayer of TMGa on Si and Au is observed with an incident wavelength of 266 nm; direct absorption by the adsorbed molecules occurs at this wavelength. At 355 nm, photodissociation does not occur.

Fine Structure Branching Ratios and Doppler Spectroscopy of Chlorine Atoms from the Photodissociation of Alkyl Chlorides and Chlorofluoromethanes at 157 and 193 nm.

Abstract: Alkyl chlorides (R=CH3, C2H5, C3H7, and C4H9), chloromethanes (CHnCl4−n), and chlorofluoromethanes (CFnCl4–n) are photodissociated at 157 and 193 nm. The chlorine atom photofragments are detected by a resonance enhanced multiphoton ionization technique. The branching ratios of the Cl photofragments [Cl*(3p2P1/2)]/[Cl(3p2P3/2)] are almost identical (0.23±0.03) for alkyl monochlorides at 157 and 193 nm and for CH2Cl2 and CHCl3 at 157 nm, while the ratios are rather small (0.10±0.02) for CH2Cl2 and CHCl3 at 193 nm. No discernible isotope effects on the branching ratios were observed when D atoms were substituted for H atoms in chloromethanes. For CCl4, CF3Cl, CF2Cl2, CFCl3 at 157 and 193 nm, the ratios are small (<0.05) irrespective of the number of Cl atoms in the parent molecules. The Doppler profiles of the chlorine photofragments have been obtained and it is found that (a) CF3Cl undergoes a perpendicular optical transition at 157 nm and (b) for halomethanes containing more than two Cl atoms, the Cl photo...