No abstract

Photofragment ion imaging has been used to study the O(1D2) atoms produced in the ultraviolet (∼200 nm) photodissociation of nitrous oxide (N2O) in a molecular beam. The images of O(1D2) reveal a speed-dependent angular distribution resulting from both variation in the spatial anisotropy of the recoil and alignment of the electronic angular momentum of the O(1D2) fragment. The orbital alignment effects are revealed by a change in the images when different transitions of the O atom are employed in the resonance enhanced multiphoton ionization (REMPI) process. By correlating the O atom anisotropies with previously measured values for the complementary N2 fragments and comparing images collected on two different REMPI transitions, we calculate the relative branching ratios and anisotropies for the three different |m| values (defined along the product recoil axis) of the electronic angular momentum of the O(1D2) fragment. While m = 0 fragments have the highest probability for most O atom speeds, there is a significant change in the alignment and angular distributions for the slower O atoms. We use a simplified dynamical model supported by previous theoretical structure calculations to explain the measured trends and to estimate the relative branching in the excitation to two N2O electronic states.

No abstract

Electronic ground-state SrF (X 2 Σ) products formed in the reaction of electronically excited Sr( 3 P 1 ) with HF are studied using laser-induced fluorescence (LIF) detection. Sr atoms are excited to the 3 P 1 state using a frequency-narrowed and -stabilized linear titanium-sapphire laser at 689.3 nm. The vibrational and rotational population distributions in the SrF(X 2 Σ) products are deduced from the LIF spectra of the B 2 Σ-X 2 Σ and A 2 Π 3/2 -X 2 Σ transitions using spectrum simulation. The results show a strong dependence of the SrF internal energy distribution on the impact parameter. The light H atom is ejected with high translational energy.

Laser-induced fluorescence spectra reveal the internal energy distributions of SrF(X 2 ⌺) formed in the reactions of electronically excited Sr( 3 P 1 ) with various unsaturated fluorohydrocarbons, i.e., CHFvCH 2 , CF 2 vCH 2 , CHFvCHF, and C 6 H 5 F. The internal energy distribution of the ground state diatomic product typically shows less vibrational excitation, without inversion, and somewhat lower rotational excitation than the reactions of Sr( 3 P 1 ) with HF and saturated hydrocarbons. The different behavior of the two groups of reactants is rationalized by a simple MO picture, assuming that an electron from Sr is transferred to a * orbital in HF and the saturated fluorohydrocarbons and to a * orbital in the unsaturated fluorohydrocarbons with a subsequent transfer to a * orbital of the C-F bond. The latter transfer constitutes an extension of the reaction path, leading to less vibrational excitation. This would explain why the energy disposal in the reaction with C 6 H 5 F behaves similar to that in the reactions with the fluoroethenes. Even if the shape of the vibrational distribution of the SrF product is the same for all unsaturated fluorohydrocarbons studied, the degree of vibrational excitation varies strongly. This even holds when comparing cis-and trans-CHFϭCHF, where the distributions can be characterized by distinct surprisal parameters.