A. Dalgarno

Molecular diagnostics of interstellar shocks

The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km s/sup -1/ Substantial enhancements are predicted in the concentrations of the molecules H/sub 2/S, SO, and SiO compared to those anticipated in cold interstellar clouds.

Sodium 2P fine-structure transitions in collisions with helium

Abstract Based upon the interaction of Baylis, a close-coupled partial-wave calculation of the cross section for fine-structure transitions in Na(3p 2 P) in collisions with He has been carried out that yields cross sections in harmony with the experimental value. The agreement provides strong support of theoretical description of the process and of the model used by Baylis to calculate the interaction.

Rayleigh-Schrödinger multiple perturbation theory

Abstract A convenient procedure is described for the solution of the equations arising in Rayleigh-Schrodinger multiple perturbation theory. Some elementary applications of the procedure are carried out.

Low-energy electrons in polar cases

Abstract The close-coupling equations describing the scattering of an electron by a rotating dipole are solved numerically for a range of energies and a range of dipole moments. The results show no anomalies in the neighborhood of the critical dipole moment.

The first-order long-range interaction between atoms

Abstract A general expression is derived for the first-order long-range interaction between atoms with one open shell. An interaction energy decreasing as the inverse fifth power of the distance with a coefficient of 2.0 × 10 −51 erg cm 5 is predicted for the b 3 Σ + state of CO, in harmony with an analysis of experimental predissociation data.

Warm hydrogen at high galactic latitudes

The physical state of gas in the transition zones between halo clouds and the hot coronal gas is investigated. The equation of state is calculated. If H/sub 2/ forms efficiently on grain surfaces, its action as a coolant can maintain an observable amount of gas at a temperature near 1000 K for a number density of the order of 1 cm/sup -3/. It is suggested that the warm H i observed at high galactic latitudes resides in these warm transition zones. The abundances of H/sub 2/, OH, and CH/sup +/ in the transition zones are discussed.

The charge transfer spectrum of (LiNa)

Abstract A model potential method is used to calculate the dipole moment of the X 2 Σ + -A 2 Σ + charge transfer transition of the molecule (LiNa) + . The corresponding absorption cross sections for low-lying vibrational levels of the X 2 Σ + state are presented as functions of wavelength. The cross sections are large in the visible region of the spectrum.