Laser-microwave two-photon and double resonance spectroscopy of two linear molecules; HCCF and FCN

Abstract

The technique of laser-microwave two-photon spectroscopy has been used to determine the frequencies of a number of transitions in fundamental and hot-bands of the two linear molecules HCCF and FCN. This method has previously only been applied in a systematic way to spectroscopy in NH 3 and it was the aim of this investigation to determine to what extent this method was applicable to more normal molecular species. The maximum effective tuning range produced with these molecules was ±3.7 GHz with a microwave power density of ⋍100 mW/cm 2 and a laser power density of ⋍40 W/cm 2. Transition frequencies were determined with accuracies up to ±3 MHz using a Lamb-dip technique. In the case of fluoroacetylene the observation of a number of double resonance signals involving direct l-type doubling transitions allowed determination of l-type doubling constants for the states ( v 3 = 1, v 4 = 1) and ( v 3 = 1, v 5 = 1). The P(12) C 18O 2 laser line was shown to lie within the Doppler width of the upper l-type doublet R(25) transition of the ( ν 3 + ν 4) − ν 3 hot band. In this particular case velocity-tuned multiple photon dips were observed. The dispersive component of double resonance and two-photon Lamb-dip signals was observed to have opposite phase in two different vibrational states. The possible diagnostic value of this observation is discussed.