The ν6 and ν8 bands of formic acid at 1104.8 and 1033.5 cm-1 were observed at 0.01 cm-1 resolution using the Kitt Peak Fourier-transform spectrometer. The ν8 Q branch was observed at 0.001 cm-1 resolution using a diode laser source. These data, together with previous laser saturation, and far-IR and microwave data have been fit with a Watson A-reduced Hamiltonian to determine excited state constants. The A-type Coriolis term was included in the fit and the total Hamiltonian was diagonalized. The new data and fit improve the accuracies of the molecular constants and allow several previously undetermined hextic distortion constants in ν8 to be obtained. We have assigned several previously unassigned far-IR laser transitions occurring between rotational levels in vibrationally excited formic acid states. The new set of constants should allow accurate assignment and prediction of other formic acid far-IR laser transitions.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry