Full-Dimensional Quantum Dynamics of SiO in Collision with H2.

We report the first full-dimensional potential energy surface (PES) and quantum mechanical close-coupling calculations for scattering of SiO due to H2. The full-dimensional interaction potential surface was computed using the explicitly correlated coupled-cluster (CCSD(T)-F12b) method and fitted using an invariant polynomial approach. Pure rotational quenching cross sections from initial states v1 = 0, j1 = 1-5 of SiO in collision with H2 are calculated for collision energies between 1.0 and 5000 cm-1. State-to-state rotational rate coefficients are calculated at temperatures between 5 and 1000 K. The rotational rate coefficients of SiO with para-H2 (p-H2) are compared with previous approximate results which were obtained using SiO-He PESs or scaled from SiO-He rate coefficients. Rovibrational state-to-state and total quenching cross sections and rate coefficients for initially excited SiO (v1 = 1, j1 = 0 and 1) in collisions with p-H2 (v2 = 0, j2 = 0) and ortho-H2 (o-H2) (v2 = 0, j2 = 1) are also obtained. The application of the current collisional rate coefficients to astrophysics is briefly discussed.

K-shell x-ray spectroscopy of atomic nitrogen.

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64±0.02 eV was determined for the K-shell binding energy.

Photoionization of metastable O+ ions: experiment and theory.

High-resolution absolute experimental measurements and two independent theoretical calculations were performed for photoionization of O+ ions from the 2P(o) and 2D(o) metastable levels and from the 4S(o) ground state in the photon energy range 30-35.5 eV. This is believed to be the first comparison of experiment and theory to be reported for photoionization from metastable states of ions. While there is correspondence between the predicted and measured positions and relative strengths of the resonances, the cross-section magnitudes and fine structure are sensitive to the choice of basis states.