Knowledge Bank

Applying an IRIR double resonance technique in a seeded molecular jet, a rotationally cooled hot band spectrum of ethane has been recorded in the region of the C-H stretching fundamental $\nu 7$ near $3000cm-1$. A mixture of $C2H6$ and $SF5$ in Ar is expanded through a slit nozzle. A 10 Watts cw $CO2$ laser excites a single rotational level in the $\nu 3$ manifold of $SF6$. Collisional relaxation redistributes the excited state population over many rovibrational levels of $C2H6$. A continuously tunable F-center laser (FCL) the probes the changes in $C2H6$ population induced by the $CO2$ laser. No evidence has been found for hot bands starting from excited torsional states indicating that these levels are quickly deactivated by V-T transfer to the ground state in the collisional environment of the jet. Significant population of high rotational levels in the ground state demonstrate rapid conversion of internal rotation into end-over-end rotation of the molecule. The $v9$ state collects substantial population suggesting that this state is collisionally rather stable. The observed hot bands are assigned to the two perpendicular components of the $\nu 7+\nu 9$ band. The spectrum appears to be heavily perturbed by dark state interactions in the upper level forcing us to analyse each K-stack separately. Rotational levels in the $\nu 7+\nu 9$ state up to $J=15$ and $K=5$ have been least squares litted to standard symmetric rotor expressions with an average standard deviation of $0.0014cm-1$.