ELECTRIC-FIELD-INDUCED Q-BRANCH OF THE VIBRATIONAL FUNDAMENTAL OF CO

The electric-field-induced Q branch of the vibrational fundamental has been observed for the first time in a polar diatomic molecule in a st udy of (CO)-C-12-O-16 near 2143.(-1) Intensity measurements of the Q(0 ), Q(1), and Q(2) transitions with a diode laser spectrometer have sho wn that these normally forbidden lines become allowed through the mixi ng of rotational levels generated by the interaction of the dipole mom ent with the externally applied electric field. Measurements have been made both with a static field and with a square-wave-modulated field. The electric dipole moment of (CO)-C-12-O-16 n the fist-excited vibra tional state, not previously measured experimentally, has been found t o equal - 0.0830 (23) D. The transition moment for the vibrational fun damental has been determined to be 0.1077 (38) D, which is in agreemen t with previous, more precise determinations based on the intensity of the allowed P and R branches. The results obtained here are in excell ent agreement with earlier calculations of the dipole moment function.