RADIATIVE LIFETIMES OF CH2(B1B1)

Radiative lifetimes are reported for CH2(b1B1) in a wide range of rotational states in the (0,14,0), (0,15,0), (0,16,0), and (0,17,0) vibrational levels. Laser photolysis of ketene in a supersonic-jet expansion produced CH2 (a1A1) which was excited to single rovibrational levels of the (b1B1) state by a second laser. Analysis of the temporal evolution of the fluorescence (b1B1)-(a1A1) yielded collision-free radiative lifetimes for the (b1B1) state. The measured lifetimes range from about 4 to 10 mus and decrease with increasing vibrational energy. For the (0,14,0) overtone, the lifetimes increase slightly as a function of J (K(a)=0). However, the lifetimes of rotational levels with K(a)=0 in the (0,16,0) vibrational state are found to be independent of the rotational state. Calculations of the vibronic lifetimes show that the considerable lifetime lengthening when K(a) greater-than-or-equal-to 1 is due to Renner-Teller coupling to the a1A1 state. The random lifetime fluctuation observed in some vibronic bands is probably due to spin-orbit coupling to the X3B1 state, e.g., 4(13) and 4(14) Of (0,15,0). Here the radiative lifetime of the singlet component is shorter than that of the corresponding triplet component.