Hydrogen Raman linewidths in supercritical water and carbon dioxide

H-2 Raman linewidths provide a probe of intermolecular potentials and have been examined in the past to explore collisional dynamic characteristics in high-pressure gas mixtures. We report the measurement of H-2 Delta v = 1 Q-branch lines, Q(0)-Q(5), and pure rotational lines, S(0)-S(5), in supercritical water and high-pressure carbon dioxide at 450 degrees C and pressures up to 50 MPa, The data are analyzed by separating the contributions to the line broadening due to different collisional processes characterized as vibrational dephasing, inelastic J-changing and rotational reorientation, The linear broadening coefficients for these different processes are determined. Both water and carbon dioxide are shown to be much more effective at disturbing H-2 rotation than other less polar molecules that have been examined in the past, Water is shown to be much more effective at causing inelastic J-changing relaxation than carbon dioxide, Elastic rotational reorientation rates are comparable for both colliders, Copyright (C) 2000 John Wiley & Sons, Ltd.