Knowledge Bank

Merging of the vibrational structures of the $A¯$ and $B¯$ electronic states of HCN and DCN into a single $A-1A\prime \prime$ $state1$, and new measurements of rotational fine structure between 1600 and 1950 {\AA}, have made it possible to attempt refinement of the molecular geometry in the $A―$ state; an attempt based on rotational constants of HCN, DCN, $D13CN$ and $DC15N$ will be described. The fine structure is mostly predissociated so that the rotational constants were determined by computer simulation of $Kv1$ sub-band contours; in the simulation process it was convenient to measure and analyze also the line-widths of unblended lines in each simulated $K01$ sub-band. It was then straight forward to estimate $A~$-state lifetimes of the DCN’s and their variations with vibrational quantum numbers. These lifetimes range from 120 to 0.4 ps; they will be compared with recently $published2$, directly measured lifetimes for lower vibrational levels of the $A―$-states of HCN and DCN.