High-resolution laser spectroscopy of the ν3 vibration-rotation band of HCOOH

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Abstract
The ν3 (C = O stretching) band of HCOOH has been studied by the techniques of CO laser Stark spectroscopy and tunable diode laser spectroscopy. The coincidence in frequency between the 13–12 P(15) CO laser line and the 110←211 transition of the ν3 band has been found by Stark spectroscopy and confirmed by laser‐microwave double resonance. It is found that the Ka = 4 and Ka = 7 levels of the ν3 state are perturbed because of Coriolis interactions with the close‐lying ν5+ν9 and ν6+ν9 states, respectively. The band origin, rotational and centrifugal distortion constants, and components of the dipole moment are determined for the ν3 state from the analysis of the unperturbed transitions. The Coriolis coupling constants and information on the interacting states are obtained from the analysis of perturbed transitions.