Sub-Doppler laser-Stark and high-resolution Fourier transform spectroscopy of the ν3 band of formic acid
The 5.6-μm band of HCOOH, which is the strong carbonyl stretch mode, is analyzed using a combination of sub-Doppler resolution laser-Stark data obtained with a CO laser and Fourier transform data obtained from a Bomem interferometer. The Fourier transform data, including 647 lines with J' ≤ 22 and Ka ≤ 11, are fit with a Watson-type Hamiltonian to determine excited state constants. The Coriolis interactions with v5+9 and v6+9, previously noted by Kuze et al., are included in the analysis; the former by using an exact diagonalization technique, the latter via perturbation theory. Taking the molecular parameters from this fit, the laser-Stark data are then analyzed to give ground and excited state dipole moments, yielding the following results in Debyes: μ″ a=1.4071(8) μ″ b=0.227(10) μ' a=1.4353(9) μ' b=0.214(9), where the errors are 3σ estimates. The laser-Stark data are limited to J' ≤ 7 and give a ± 14 MHz fit to 191 lines.