Cavity-enhanced absorption spectroscopy of the 1.5 μm band system of jet-cooled ammonia

Absorption spectra of rotationally cold ammonia (14NH3) molecules have been recorded in the 6400–6630 cm−1 region, using the cavity-enhanced absorption technique in combination with a slit-nozzle expansion. Two perpendicular rovibrational bands have been identified: the ν1+ν3 band at 6609 cm−1, and a `newʹ band at 6557 cm−1 which is tentatively assigned to a transition into the |l|=2 component of the ν1+2ν4 state.