Raman pump/probe measurements of state-to-state energy transfer rates in the v=1 state of H2

We have measured state-resolved rotational energy transfer rates of H2 (v=1) in collisions with H2 (v=0) at 295 K, using optical pump/probe techniques. A single rotational level was populated using stimulated Raman pumping, and the degree of collision-induced population transfer was monitored using either coherent anti-Stokes Raman spectroscopy (CARS) or resonance-enhanced multiphoton ionization spectroscopy (REMPI). The CARS and REMPI results are in good agreement; averages of the two sets of rates are 180±27×106 s−1 amagat−1 for j=0→2 and 50±8×106 s−1 amagat−1 for j=1→3. We also observed transfer of vibrational excitation from paraspin v=1 states to ortho v=0 states due to v–v exchange, measuring a rate of 1.9±0.8×106 s−1 amagat−1 for this process.