Vibrational Energy Transfer in Ortho and Para NH3

Abstract

<p> An experimental study of vibrational energy transfer in ortho and para NH3(v2) is presented. The vibrational relaxation rates are necessary to characterize mid-IR pulsed and cw NH3 lasers, and the interpretation of these rates is of theoretical importance. Accurate information on the (V-T) process in NH3/N2 mixtures and the (V-V) energy transfer between ortho and para 15NH3 and 14NH3 is now available. </p> <p> First, NH 3 linestrengths and linewidths were accurately measured with a tunable diode laser (TDL) so that ammonia concentrations could be calculated from TDL scans. The energy transfer mechanisms were studied by exciting the v2 vibration of NH3 with a Q-switched cO2 laser and probing the subsequent changes in population with a TDL. A difference in v 2 lifetimes was observed between ortho and para NH3 transitions, and is explained by a (V-V) transfer of energy between the NH3 species. An isolated ortho 15NH3 absorption line was pumped and vibrational transfer of energy was observed to ortho and para 14NH3 and 15NH3. </p>