Time-domain investigation of OH ground-state energy transfer using picosecond two-color polarization spectroscopy

Two-color polarization spectroscopy was used to investigate rotational energy transfer (RET) and relaxation of orientation and alignment in the ground electronic state of OH in an atmospheric-pressure methane–air flame. Two independently tunable lasers produced nearly transform-limited infrared and ultraviolet pulses of 50 ps duration. The infrared laser excited rovibrational transitions, and delayed ultraviolet pulses probed electronic transitions from either the directly pumped or collisionally populated states. Alignment and orientation relaxation times were measured for individual rotational levels in OH X2Π3/2(v=1), and the feasibility of time-domain investigation of state-to-state energy transfer processes was demonstrated.