State-to-state and total rotational energy transfer rate constants for CN(B (2)Sigma(+),v=0,N)+He and C2N2

Total rotational energy transfer (RET) rate constants, state-to-state RET r ate constants, and radiative lifetimes have been measured for CN(B (2)Sigma (+), upsilon =0, N-i=0, 4, 6, 7, 8, 11 and 13). All experiments were condu cted under single collision conditions in a static cell filled with previou sly prepared C2N2/He mixtures at various total pressures up to a maximum of 800 mTorr. The above initial states were prepared by pumping CN(X) with a pulsed dye laser tuned to appropriate frequencies in the P-branch of the CN -violet (0,0) band following the production of CN(X) by the excimer laser p hotolysis of C2N2 at 157 nm. Total RET rate constants and radiative lifetim es were determined from decay constants obtained with a transient digitizer over the above range of cell pressures. State-to-state RET rate constants were obtained from time-averaged fluorescence spectra in the R branch of th e (0,0) band of the CN violet system at various cell pressures within the a bove range. A weak propensity for odd jumps in N was discernable in state-t o-state RET rate constants in CN(B)/He collisions for N >4. Total RET rate constants varied only slightly with N-i for 0 less than or equal toN(i)less than or equal to 19 with He as collision partner, but decreased monotonica lly with increasing N-i when C2N2 served as collision partner. No firm evid ence for collisionally induced CN(B)<----> CN(A) was apparent from our data . (C) 2000 American Institute of Physics. [S0021-9606(00)01341-6].