Cutoff Theory of Impact Broadening and Shift.

An impact theory of pressure broadening and shift of rotation-vibration lines using a natural cutoff is described. The theory is based on Anderson's theoretical framework and employs an exponential expansion of the collision matrix elements derived using a linked cluster theorem for degenerate states. The final expression for the interruption function is similar in form to Gordon's classical interruption function. Closed form expressions for the broadening and shift cross sections are given for exactly resonant dipole-dipole collisions, and a calculation of the HCl self-broadening in the 0-2 vibrational band is given.