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

Total rotational energy transfer (RET) rate constants, state-to-state RET rate 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 conducted under single collision conditions in a static cell filled with previously 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 photolysis of C2N2 at 157 nm. Total RET rate constants and radiative lifetimes 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 the (0,0) band of the CN violet system at various cell pressures within the above range. A weak propensity for odd jumps in N was discernable in state-to-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 monotonically with increasing N-i when C2N2 served as collision partner. No firm evidence for collisionally induced CN(B)<----> CN(A) was apparent from our data. (C) 2000 American Institute of Physics. [S0021-9606(00)01341-6].