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The speed and angular distribution of O atoms arising from the photofragmentation of C(5)H(8)-O(2), the isoprene-oxygen van der Waals complex, in the wavelength region of 213-277 nm has been studied with the use of a two-color dissociation-probe method and the velocity map imaging technique. Dramatic enhancement in the O atoms photo-generation cross section in comparison with the photodissociation of individual O(2) molecules has been observed. Velocity map images of these "enhanced" O atoms consisted of five channels, different in their kinetic energy, angular distribution, and wavelength dependence. Three channels are deduced to be due to the one-quantum excitation of the C(5)H(8)-O(2) complex into the perturbed Herzberg III state ((3)Δ(u)) of O(2). This excitation results in the prompt dissociation of the complex giving rise to products C(5)H(8)+O+O when the energy of exciting quantum is higher than the complex photodissociation threshold, which is found to be 41740 ± 200 cm(-1) (239.6±1.2 nm). This last threshold corresponds to the photodissociation giving rise to an unexcited isoprene molecule. The second channel, with threshold shifted to the blue by 1480 ± 280 cm(-1), corresponds to dissociation with formation of rovibrationally excited isoprene. A third channel was observed at wavelengths up to 243 nm with excitation below the upper photodissociation threshold. This channel is attributed to dissociation with the formation of a bound O atom C(5)H(8)-O(2) + hv → C(5)H(8)-O(2)((3)Δ(u)) → C(5)H(8)O + O and/or to dissociation of O(2) with borrowing of the lacking energy from incompletely cooled complex internal degrees of freedom C(5)H(8)*-O(2) + hv → C(5)H(8)*-O(2)((3)Δ(u)) → C(5)H(8) + O + O. The kinetic energy of the O atoms arising in two other observed channels corresponds to O atoms produced by photodissociation of molecular oxygen in the excited a (1)Δ(g) and b (1)Σ(g)(+) singlet states as the precursors. This indicates the formation of singlet oxygen O(2)(a (1)Δ(g)) and O(2)(b (1)Σ(g)(+)) after excitation of the C(5)H(8)-O(2) complex. Cooperative excitation of the complex with a simultaneous change of the spin of both partners (1)X-(3)O(2) + hν → (3)X-(1)O(2) → (3)X + (1)O(2) is suggested as a source of singlet oxygen O(2)(a (1)Δ(g)) and O(2)(b (1)Σ(g)(+)). This cooperative excitation is in agreement with little or no vibrational excitation of O(2)(a (1)Δ(g)), produced from the C(5)H(8)-O(2) complex as studied in the current paper as well as from the C(3)H(6)-O(2) and CH(3)I-O(2) complexes reported in our previous paper [Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. The formation of O(2)(a (1)Δ(g)) from C(5)H(8)-O(2) was observed at λ(pump) = 213-277 nm with the yield going down towards the long wavelength edge of this interval. This spectral profile is interpreted as the red-side wing of the band of a cooperative transition (1)X-(3)O(2) + hν → (3)X(T(2))-(1)O(2)(a (1)Δ(g)) in the C(5)H(8)-O(2) complex.

The discrete Kohn variational reactive scattering method presented in the preceding paper is applied to the reaction H+O2→ OH+O. The essential features of the method are the use of an interaction region grid, fully coupled open and closed distorted waves (DWs) and the use of a singular value decomposition technique to construct the optimal boundary conditions for the open DWs. A convergence test is presented at a total energy of 0.817 eV above the bottom of the H+O2 well. It is shown that very well converged results may be obtained in a calculation with a relatively small interaction region grid, when at least a few asymptotically closed DWs are included in the trial wave function. Furthermore, the number of open distorted waves (DWs) may be considerably smaller than the number of open channels. Six additional points are computed in an energy range of 1.2 meV, scanning through a narrow resonance around 0.817 eV. The results are in very good agreement with the hyperspherical coordinate propagation calculat...

In this paper, we report the first rotationally resolved one- and two-color resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the HCl molecule. The agreement between our experimental branching ratios and theoretical investigations is excellent. We also report the first zero kinetic energy pulsed field ionization (ZEKE-PFI) experiments carried out in a "magnetic bottle'' electron spectrometer. A direct comparison is made between ZEKE-PFI and REMPI-PES spectra for ionization via several rotational levels of the F 12(v'=0) and f 32(v'=0) Rydberg states of HCl. Large differences in both the spin-orbit and rotational branching ratios are found between the ZEKE-PFI and REMPI-PES spectra. These differences can be understood qualitatively on the basis of rotational and spin-orbit autoionization mechanisms. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

A new effective Hamiltonian is presented for the analysis of the high-resolution spectra of open-shell van der Waals complexes containing the O2 molecule. The effects of electron spin are included but the complications of nuclear spin and resultant nuclear spin splitting are neglected. The Hamiltonian is composed of the rotational, centrifugal distortion, and spin-spin interaction terms. The resulting energy levels are divided into two well-separated groups and the pattern is a complicated function of θ (the angle that the O2 molecule makes with the principal a axis of the complex) and φ (the azimuthal angle of the O2 out of the plane defined by the a and b axes of the complex). This model has been successfully applied to analyze the high-resolution spectrum of O2-N2O in the region of the N2O monomer ν3 vibrational band, which will be presented in a separate paper. © 1997 American Institute of Physics.