High-resolution FTIR spectroscopy of H13COOD: The ground state and v2 = 1 state rovibrational constants

Abstract

The Fourier transform infrared (FTIR) rovibrational spectrum of the ν2 band of the formic acid isotopologue H13COOD was recorded in the 2550–2710 cm−1 region at an unapodized resolution of 0.0063 cm−1. Rovibrational constants up to three quartic terms were derived for the first time with high precision for the v2=1 state through the fitting of 626 infrared transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.0023 cm−1. The rotational energy levels of the ν2 band was found to be perturbed by a nearby 3ν7 + ν8 band. From the analysis, a- and b-Coriolis resonance parameters from the interactions of the ν2 band with 3ν7 + ν8 band were obtained for the first time. The rotational constants A and B along with the band center of the 3ν7 + ν8 band were also derived for the first time in this work. The band centers of the ν2 and 3ν7 + ν8 bands of H13COOD were determined as 2631.13155(34) cm−1 and 2596.31(19) cm−1 respectively. The ground state constants of H13COOD were determined with higher precision than previously by fitting 301 ground state combination-differences (GSCDs) from the present work and 24 previous microwave measurements with rms deviation of 0.00073 cm−1. The equilibrium state rovibrational constants up to five quartic terms were derived from theoretical anharmonic calculations at four levels of theory: MP2/cc-pVTZ, B3LYP/cc-pVTZ, MP2/cc-pVQZ and B3LYP/cc-pVQZ using the principal axis coordinate system. These calculated constants agree with the ground state constants of H13COOD derived from the current experimental GSCD combined with microwave transitions fit. In addition, all three rotational constants (A, B and C) of the ground state of H13COOD were obtained from anharmonic calculations using B3LYP and MP2 levels with the cc-pVTZ and cc-pVQZ basis sets. These rotational constants were found to agree with those derived experimentally with percentage deviations within 1.0%.