First assignments of the 6ν4, ν2+5ν4, and ν1+4ν4 Triacontad band system of 12CH4 in the 7606-7919 cm−1 region

Abstract

Quantum assignments are reported for 1382 transitions towards 33 vibrational sub-levels belonging to three weak Triacontad bands 6ν4, ν2+5ν4, ν1+4ν4 of 12CH4 1.28µm. Empirical values of the origins of the corresponded sub-bands were determined for the first time from high resolution spectra analysis. The positions of all assigned lines were fitted to a model adopting an effective Hamiltonian whose initial values are derived from the molecular potential energy surface by using the contact transformation method. An empirical optimization of this effective model resulted in the root-means-square deviation of 0.006 cm−1 for newly assigned transitions. A comparison with variational ab initio calculations is discussed.