NEW SUBMILLIMETER CW LASER LINES IN OPTICALLY PUMPED GAS MOLECULES -- ASSIGNMENT OF THE FORMIC ACID LASER

Author Institution: Laboratoire de Spectroscopie Hertzienne, Universit\'{e} de LilleA submillimeter laser optically pumped by a $CO_{2}$ laser has been built and cw laser action has been observed from 1033 to 195 $\mu m$ in several molecules: $D_{2}CO$, HDCO, $(H_{2}CO)_{3}$, DCOOD, $H^{13}COOH$, HCOOD. In the case of $H^{12}COOH$ the accurate measurements of 18 cw laser lines from 380 to 1000 GHz has been performed by measuring the beat notes of the mixing of the harmonics of a phase locked millimeter source with the laser emission. The accuracy of the measurements is about 0.5 to 1 MHz. The assignment of the formic acid laser lines needs detailed spectra of ground and vibrationally excited states. The ground state is well known. An experimental improvement of the pure rotational spectra of the $\nu_{6} (1105 cm^{-1})$ and $\nu _{8} (1033 cm^{-1})$ vibrationally excited states has been necessary. The $CO_{2}$ pumping is performed from ground state levels up to excited states. Most of the laser emission lines have been assigned to the $\nu_{6}$ excited state; it is thus possible to derive a very good value for the band center of this state."