Vibrational energy transfer from C2H4 to CO2 studied at low temperatures in a jet by infrared double resonance

In a mixed CO2-C2H4 jet the populations of rotational levels in the ground andv2 (667 cm−1) vibrational state of CO2 are probed by color center laser absorption. The rotational distributions are well described by a rotational temperature. On the timescale of the expansion thev2 state does only relax through resonant deexcitation by CO2 clusters. A 10% fraction of C2H4 molecules is excited into thev7 (949 cm−1) level by CW CO2 laser absorption, subsequently releasing energy into the expansion due to relaxation to lower C2H4 vibrational states and to thev2 mode of CO2. Observed are the induced rise of rotational temperature and the increase ofv2 level population. By probing at several distances from the nozzle the temperature range from 30–155 K is covered. The vibrational transfer of the excited C2H4 to thev2 level of CO2 has a near quadratic inverse temperature dependence, increasing by a factor of 40 when the temperature is lowered from 155 K to 30 K.