Study of the ν3 band of 12CD4: Line position analysis and unambiguous fit of q2J4 terms

Abstract

We report the analysis of 12CD4 line positions from high-resolution rovibrational spectra, including accurate lines in the region 2160–2360cm−1. In this analysis, 181 data points are fitted using an effective Hamiltonian expanded up to the sixth order for the ν3 fundamental band. For the assignments and analysis, we use the SPVIEW and XTDS software programs that implement the tensorial formalism developed in the Dijon group for tetrahedral molecules. Experimental transitions are assigned up to J⩽15 for the ν3 cold band. Among the 37 parameters of the effective Hamiltonian for the ν3 fundamental band (of which 10 are relative to the Ground State (GS or P0), and 27 are relative to ν3), 22 relative to ν3 were fitted. The 32 parameters for ν3 allow very good simulations to be made. For this study, a total of 181 line positions were used in the least squares adjustment characterized by the root mean square deviation dRMS for line positions: 1.196×10−3cm−1. On the basis of our set of 181 fits of experimental data for ν3 of 12CD4, the ambiguity of effective Hamiltonians for triply degenerate F2 states of tetrahedral molecules is verified. It is shown that, in agreement with theory, any of q2J4-type parameters cannot be determined from experimental data in a unique way, and these parameters cannot be considered as spectroscopic constants.