TG14		15 min5:07

W. LEO MEERTS, JOS OOMENS AND JÖRG REUSS, Department of Molecular and Laser Physics, Catholic University of Nijmegen, Toernooiveld 1, 6525ED Nijmegen, The Netherlands.

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 \seven near 3000~cm^-1 . A mixture of \ethane and \sfsix in Ar is expanded through a slit nozzle. A 10 Watts cw \co laser excites a single rotational level in the \three manifold of \sfsix . Collisional relaxation redistributes the excited state population over many rovibrational levels of \ethane . A continuously tunable F-center laser (FCL) then probes the changes in \ethane population induced by the \co 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 \nine 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 ₇+₉(A_1g\oplus A_2g\oplus E_g)<- ₉(E_u) 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 \sevnine state up to J=15 and K=5 have been least squares fitted to standard symmetric rotor expressions with an average standard deviation of 0.0014 cm^-1 .