The nu(7)+nu(9)-nu(9) hot band in ethane

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 v(7) near 3000 cm(-1). The observed hot bands are assigned to the two perpendicular components of the v(7) + v(9)(A(1g) + A(2g) + E(g)) <-- v(9)(E(u)) band. The spectrum appears to be heavily perturbed by dark state interactions in the upper state, forcing us to analyze each K-stack separately. Rotational levels in the v(7) + v(9) 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). No evidence has been found of 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; however, the vg state collects a substantial population, suggesting that this state is collisionally rather stable. (C) 1996 Academic Press, Inc.