Showing papers by "Mitchio Okumura published in 2003"
TL;DR: In this paper, a low-pressure discharge flow reactor was used to study the termolecular association reaction OH + NO2 + M and both HONO2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS).
Abstract: The termolecular association reaction OH + NO2 + M was studied in a low-pressure discharge flow reactor, and both HONO2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental ν1 band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm-1, in good agreement with matrix isolation studies and ab initio predictions. The rotational contour of this band was partially resolved at 1 cm-1 resolution and matched the profile predicted by ab initio calculations. The integrated absorbances of the ν1 bands of the cis-cis HOONO and HONO2 products were measured as a function of temperature and pressure. These were converted to product branching ratios by scaling the experimentally observed absorbances with ab initio integrated cross sections for HOONO and HONO2 computed at the CCSD(T)/cc-pVTZ level. The product branching ratio for cis-cis HOONO to HONO2 was 0.075 ± 0.020(2σ) at room temperature in a 20 Torr mixtu...
45 citations
11 Sep 2003
TL;DR: In this paper, an experimental and theoretical analysis of the multiphoton ionization spectroscopy of selected AlAr_N clusters (N = 2−54) was performed using a laser-ablation/pulsed supersonic expansion source.
Abstract: Experimental and theoretical studies are reported of the multiphoton ionization spectroscopy of selected AlAr_N clusters (N = 2−54). Resonantly enhanced 1_(uv) + 1_(vis) and 2_(vis) + 1_(vis) ionization spectra are recorded of neutral clusters employing a laser-ablation/pulsed supersonic expansion source and time-of-flight mass spectrometric cluster-ion detection. The spectra are dominated by broad red- and blue-shifted asymmetric bands in the neighborhood of the 308 and 303 nm atomic Al 3p → 3d and 4p lines. The detailed structures of these bands and the observed degree of their spectral shifts with increasing cluster size are attributed on the basis of concomitant ab initio theoretical calculations to interplay among a number of factors, including (i) the comparable strengths of spin−orbit-split anisotropic (^2P_(1/2))Al−(^1S_0)Ar interactions and Ar−Ar mutual attractions, responsible for predicted external-site Al atom locations on distorted icosahedral Ar_N structures, (ii) avoided crossings in the nearly degenerate AlAr_N potential energy surfaces accessed by one- and two-photon atomic Al 3p → 3d and 4p excitations, giving rise to the red- and blue-shifted spectral profiles, and (iii) significant dynamical rearrangement and parent cluster-ion fragmentation following ionization, resulting in Al+Ar_M signals that generally reflect the absorption cross sections of an ensemble of larger prior clusters (AlAr_N, N > M). Additionally, nonuniformity in the cluster-size distribution of the incident molecular beam is inferred from the calculated and measured spectra and must be incorporated in the development for a completely satisfactory accounting between theory and experiment. Comparisons with the results of earlier experimental studies of the ionization potentials of AlAr_N clusters also underscore the importance of dynamical parent-ion rearrangement and fragmentation, consequent of the increased Ar solvation of the Al+ radical in the equilibrium Al+Ar_M cluster-ion structures. The reported multiphoton ionization cluster-ion spectra are evidently highly sensitive to the details of the atomic Ar arrangements around the Al chromophore and accordingly provide a spectroscopic probe of the nature and evolution of the Al trapping sites and cluster geometries with increasing cluster size when the complex electronic and vibrational phenomena underlying the measurements are appropriately interpreted.
8 citations
TL;DR: In this paper, the multihopon ionization spectroscopy of selected AlArN clusters (N = 2−54) is reported, which is dominated by broad red and blue-shifted asymmetric bands in the neighborhood of the 308 and 303 nm atomic Al 3p → 3d and 4p lines, and the detailed structures of these bands and the observed degree of their spectral shifts with increasing cluster size are attributed on the basis of concomitant ab initio theoretical calculations.
Abstract: Experimental and theoretical studies are reported of the multiphoton ionization spectroscopy of selected AlArN clusters (N = 2−54). Resonantly enhanced 1uv + 1vis and 2vis + 1vis ionization spectra are recorded of neutral clusters employing a laser-ablation/pulsed supersonic expansion source and time-of-flight mass spectrometric cluster-ion detection. The spectra are dominated by broad red- and blue-shifted asymmetric bands in the neighborhood of the 308 and 303 nm atomic Al 3p → 3d and 4p lines. The detailed structures of these bands and the observed degree of their spectral shifts with increasing cluster size are attributed on the basis of concomitant ab initio theoretical calculations to interplay among a number of factors, including (i) the comparable strengths of spin−orbit-split anisotropic (2P1/2)Al−(1S0)Ar interactions and Ar−Ar mutual attractions, responsible for predicted external-site Al atom locations on distorted icosahedral ArN structures, (ii) avoided crossings in the nearly degenerate AlAr...
7 citations