Observation of the ν3 fundamental band of HCO+

The ν3 (C–O stretching) band of HCO+ has been detected using a tunable diode laser spectrometer and a liquid nitrogen cooled hollow cathode absorption cell. Eight lines in the R branch, ranging from R(6) to R(17) were measured with an accuracy of 0.001 cm−1. Combining these data in a least-squares fit with the previously measured v3=1, J=1←0 microwave transition, the following parameters were determined: ν0=2183.9496 cm−1, B=44 299.904(10) MHz, and D=82.96(13) kHz.