SUB-DOPPLER LASER STARK SPECTRA OF THE $\nu_{3}$ BAND OF FORMIC ACID

$^{1}$ G. Guelachvili, D. de Villeneuve, R. Farrenq, W. Urban, and J. Verges, J. Mol. Spectrosc. 98, 64 (1983).Author Institution: Physics Department, Research Staff, Ford Motor CompanyStark-tuned Lamb-dip spectra of HCOOH in the $1750-1790 cm^{-1}$ region were obtained using a CO laser and an intracavity Stark cell. Approximately 40 laser lines from 4 isotopes of CO were used, and the maximum Stark field was 35 kV/cm. Several thousand individual Lamb dips were observed, only a small fraction of which have been assigned. On the basis of data from 30 resonances associated with various P(5), P(2), R(2), Q(1), and Q(2) lines, analyzed using the CO laser frequencies of Guelachvili et al., we have determined a preliminary value for the a-component of the excited state dipole moment, $\mathcal{M}_{a} = 1.420 \pm 0.005 D$. Preliminary values for the excited state molecular constants have also been obtained. Analysis of the spectrum is complicated by a perturbation occurring around $K=4$ in the excited state. Most spectra recorded near the band center show intense zero-field level crossing resonances. These appear in both parallel and perpendicular polarizations, indicating that collisional transfers are very significant