A theory of microwave lineshifts

The Anderson theory of pressure broadening of spectral lines in the microwave region (1949) is extended to permit calculations of the shifts of spectral lines. The extension is based on the analytic evaluation of double integrals. Mathematical details are presented for the dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions. The theory is used to calculate the widths and shifts, over a temperature range from 150K to 500K, of the ammonia J=K=3-8 inversion lines perturbed by NH 3 , COS and CH 3 Cl, and of the self-perturbed CH 3 Cl(J=0 to 1) and COS(J=1 to 2) rotational lines.