Knowledge Bank

Time-resolved Fourier transform emission spectroscopy spectra of the $CH2b-1B1\to a¯1A1$ band were recorded after pulsed excitation of a single rotational level of the $b-1B1(0.160,0)$ state. The temporal behavior of emission from the initially excited level and from levels populated by rotational energy changing collisions with the bath gas (ketene) was used to deduce the state-to-state cross-sections for rotational energy transfer and the state-resolved cross-sections for reactive collisions between $b-1B1CH2$ and ketene. The observed propensity rules for rotational energy transfer $\Delta J=\pm 2.\Delta K4=0$. and $\Delta Ke=\pm 2$ indicate a quadrupole-dipole interaction between $b-1B1(0,160,0)CH2$ and ketene. The bent $CH2$ excited above the bending barrier behaves like a linear molecule. The reactive cross-sections for the $CH2b-1B2$ state, which is shown to be more reactive than the $a¯1A1$ state, increase with rotational energy.