Local mode involvement in the vibrational relaxation of isolated (O2)2 dimers

Study of five isotopic species of isolated (O2)2 dimer in solid neon host near 4.2 °K shows that the mechanism of 1Δg+1Δg excited state vibrational relaxation involves intersystem crossing into the 3Σ−g+1Σ+g state. Several reversible dynamic equilibria are observed between nearly degenerate 1Δg+1Δg and 3Σ−g+1Σ+g vibronic states. Indirect arguments suggest that the nearest neighbor, nonresonant vibrational energy transfer time from 16O2(1Δg) to 18O2(1Δg) is order-of-magnitude 10−9–10−10 s. Vibrational relaxation rates for (0+v) 3Σ−g+1Σ+g states (v?3) are slower with heavier reduced masses. The relaxation rate depends not only on the nuclei in the excited O2, but also on the nuclei in the unexcited nearest neighbor O2. These results are consistent with O2 rotation accepting energy during the vibrational relaxation process. This appears to be the first such observation for a nonhydride molecule in condensed phase. The relation between spectral polarization and rotation as the accepting mode is discussed.