STATE-TO-STATE ROTATIONAL ENERGY-TRANSFER AND REACTION WITH KETENE OFHIGHLY VIBRATIONALLY EXCITED (B)OVER-TILDE B-1(1) CH2 BY TIME-RESOLVED FOURIER-TRANSFORM EMISSION-SPECTROSCOPY

Dispersed fluorescence spectra from the CH2 b B-1(1) --> a 1A1 band we re recorded with time-resolution by Fourier transform emission spectro scopy after pulsed excitation of a single rotational level of the b B- 1(1) (0,16(0),0) state. Fluorescence observed from the initially excit ed level and from levels populated by rotational energy changing colli sions with the bath gas (ketene) was used to deduce the state-to-state rate constants for rotational energy transfer and the state-resolved rate constants for total collisional removal of b B-1(1) CH2. The obse rved propensity rules for rotational energy transfer-DELTAJ = +/- 2, D ELTAK(a) = 0, and DELTAK(c) = +/- 2-are consistent with a quadrupole-d ipole interaction between b B-1(1) (0,16(0),0) CH2 and ketene. The exi stence of a quadrupole in the intermolecular interaction suggests that the structure of CH2 in the b B-1(1) (0,16(0),0) state, averaged over the time of a collision, must be linear. The state-to-state rotationa l energy transfer rate constants range from approximately equal to the hard sphere gas kinetic rate to four times the gas kinetic rate, with the largest rate constants between rotational levels with the smalles t energy gaps. Examination of fluorescence spectra recorded with polar ization analysis shows that rotationally elastic (DELTAJ = 0)M changin g collisions are negligible. State-resolved rate constants for reactiv e collisions between b B-1(1) CH2 and ketene were obtained by subtract ing the rotational approximately energy transfer contribution from the total rate constants for collisional removal of b B-1(1) CH2 (obtaine d from a Stern-Volmer analysis). These rate constants vary from one to five times the hard sphere gas kinetic rate, and increase with rotati onal energy for the levels studied. Their magnitudes show that CH2 is about two times as reactive in its b B-1(1) state than its a 1A1 state .