Observation of Vibrational Relaxation Dynamics in X3∑g Oxygen following Stimulated Raman Excitation to the v=1 Level: Implications for the RELIEF Flow Tagging Technique

The vibrational relaxation of ground-state molecular oxygen (O2, XΣg −) has been observed, following stimulated Raman excitation to the first excited vibrational level (v=1). Time delayed laser-induced fluorescence probing of the ro-vibrational population distribution was used to examine the temporal relaxation behavior. In the presence of water vapor, the relaxation process is rapid, and is dominated by near-resonant vibrational energy exchange between the v=1 level of O2 and the ν2 bending mode of H2O. In the absence of H2O, reequilibration proceeds via homogeneous vibrational energy transfer, in which a collision between two v=1 O2 molecules leaves one molecule in the v=2 state and the other in the v=0 state. Subsequent collisions between molecules in v=1 and v>1 result in continued transfer of population up the vibrational ‘ladder.’ The implications of these results for the RELIEF flow tagging technique are discussed.