A high precision technique for pressure lineshift measurements: application to NH 3 and HCN

Abstract

High precision pressure-induced lineshifts have been measured by a technique involving an infrared diode laser which is frequency stabilized on the absorption peak of the molecular line under study. The corresponding frequency shifts of the stabilized laser are discriminated by means of a reference absorbing cell filled with the same active gas set at a fixed pressure. This avoids any reference to absolute or secondary frequency standards and allows a very high sensitivity for the determination of small lineshift parameters (down to 10 kHz Torr −1 with a 10 Torr explored pressure range). As an application, H 2, He and self-induced lineshifts of the v 2 and (2 v 2− v 2) band of NH 3 and of the v 2 band of HCN have been determined.