We present calculations of cross sections for fine-structure excitation in collisions of carbon and silicon ions in the 2 P state with atomic hydrogen in the ground state. The results are based on accurate calculations of CH + and SiH + molecular potentials, including electronic core correlation and relativistic effects. We find that the energy dependence of the excitation cross sections is largely determined by shape resonances. Our work improves on the results of previous calculations with less accurate potentials. Analytical expressions for the cooling efficiency of C + (2 P 1=2) and Si + (2 P 1=2) are given for the temperature interval 15-2000 K.

No abstract

3D wave packet calculations on the CH2I2 and OClO molecules have been performed for a total angular momentum equal to zero. The initial wave function is found by solving the time independent Schrödinger equation in internal bond coordinates. The split operator method and the fast Fourier transform in hyperspherical coordinates are used in order to follow the quantum dynamics. An absorption spectrum of CH2I2 is obtained and compared with a previous 2D calculation. A Raman spectrum for the CH2I2 molecule at 355 nm is calculated and compared with experimental results. The absorption spectrum for the X2B1→A2 A2 transition of the OClO molecule is calculated using the same method as for CH2I2. Good agreement with experiment is obtained.

We demonstrate that chemical reactions in collisions of molecular beams can generally produce low-velocity molecules in the laboratory-fixed frame. Our analysis shows that collisions of beams may simultaneously yield slow reactant molecules and slow products. The reaction products are formed in selected rovibrational states and scattered in a specific direction, which can be controlled by tuning the kinetic energies of the incident beams and the angle between the beams. Our calculations indicate that chemical reactions of polar alkali-metal dimers are barrierless and we suggest that chemical reactions involving alkali-metal dimers may be particularly suitable for producing slow molecules in crossed beams.