VERY LOW-TEMPERATURE HELIUM PRESSURE BROADENING OF DCL IN A COLLISIONALLY COOLED CELL

Very low temperature pressure broadening parameters and cross sections for the J = 0-1 rotational transition of DCl broadened by helium are presented. Data was taken using a collisionally cooled cell and measured cross sections range from 10.76 angstrom 2 at 4.21 K to 8.10 angstrom 2 at 1.85 K. This compares with a 300 K cross section of 9.36 angstrom 2. Predictions from two currently available anisotropic He-DCl potentials do not reproduce accurately the experimental results. Modifications were made to one of these potentials to reproduce more accurately both the observed low temperature and 300 K pressure broadening cross sections. The resulting modified potential has a well depth D(e) = 32.7 cm-1 at a separation R(e) = 3.46 angstrom in the linear He-Cl-D configuration.