Ro-vibration transitions of the protonated argon ion

Given the atmospheric opacity at the frequency of its J=1-0 and J=2-1 rotational transitions (617.5 and 1234.6GHz, respectively), and the current lack of appropriate space observatories after the recent end of the Herschel mission, future studies on this molecule will rely on mid-infrared observations. We report on accurate wavenumber measurements of ^36^ArH^+^ and ^38^ArH^+^ rotation-vibration transitions in the v=1-0 band in the range 4.1-3.7{mu}m (2450-2715/cm).

The wavenumbers of the R(0) transitions of the v=1-0 band are 2612.50135+/-0.00033 and 2610.70177+/-0.00042/cm(+/-3{sigma}) for ^36^ArH^+^ and ^38^ArH^+^, respectively. The calculated opacity for a gas thermalized at a temperature of 100K and with a linewidth of 1km/s of the R(0) line is 1.6x10^-15^xN(^36^ArH^+^). For column densities of ^36^ArH^+^ larger than 1x10^13^/cm^2^, significant absorption by the R(0) line can be expected against bright mid-IR sources.