15min:

ZHENHONG YU, TODD A. STONE, CHENG-CHI CHUANG, WALTER DRISDELL AND WILLIAM KLEMPERER, Harvard University, Department of Chemistry and Chemical Biology, Cambridge, Massachusetts, 02138.

HF-CO₂ is quasilinear at the vibrational ground state and becomes a semi-rigid bent species at _HF = 3 with the CO₂ intermolecular bending frequency of 24.75(10) cm^-1. The ab initio potential surface is very flat from = 0 to 40^\circ at _HF = 0 while at _HF = 3 the potential energy of linear geometry is about 50 cm^-1 higher than that at the minimum near = 40^\circ. The observed features at 11174.45, 11168.10, and 11181.82 cm^-1 have been assigned to parallel transition to the K = 0, 1, and 2 levels of the second overtone HF valence band, respectively, indicating a vibrational redshift of 198.36(5) cm^-1 compared to the HF monomer. The relatively strong transition intensities of the K subbands are due to the inertial axes switching. The rotational constants of the (3000000) state are A = 2.96(2) cm^-1, (B+C)/2 = 0.0742(10), 0.0717(10), and 0.0696(10) cm^-1 for the K = 0, 1, and 2 levels. The centrifugal distortion D_K = 0.270(5) cm^-1 is extremely large but in good agreement with the expectation, as a result of very soft CO₂ intermolecular bending. The spectral linewidths are 9.0(9), 7.2(6), and 4.5(6) GHz for the above levels, showing dramatic dependence of vibrational predissociation lifetime upon K. A perpendicular transition of the HF bending combination band at 11538.92 cm^-1 provides a bending frequency of 362.77(15) cm^-1, while (B+C)/2 = 0.0668(10) cm^-1 and = 4.2(6) GHz.