Accurate laboratory measurements of vibration-rotation transitions of 36ArH+ and 38ArH+

Abstract

The protonated Ar ion 36ArH+ has recently been identified in space,a in the Crab Nebula, from Herschel spectra. Its R(0) and R(1) transitions lie at 617.5 and 1234.6 GHz, respectively, where atmospheric transmission is rather poor, even for a site as good as that of ALMA. As an alternative, especially after the end of the Herschel mission, rovibrational transitions of ArH+ could be observed in absorption against bright background sources such as the galactic center, or other objects. We report on accurate laboratory wavenumber measurements of 19 lines of the v = 1-0 band of 36ArH+ and 38ArH+, using a hollow cathode discharge cell, a difference frequency laser spectrometer and Ar with natural isotopic composition. Of those lines, only eight had been reported before and with much less accuracy.b The data have also been used in a Dunham-type global fit of all published laboratory data (IR and sub-mm) of all isotopologues.