Thermodynamic properties of vanadium and cobalt argide ions, VAr⁺ and CoAr⁺

The positive ions of 3d metal and argon compounds (metal argide ions, MAr⁺) play essential role in the mass spectrometry with argon plasma sources. At the same time their thermodynamical properties are still not sufficiently studied. Rough estimations of the internal partition functions of MAr⁺ have been made by Witte and Houk in order to calculate the concentration ratio between metal and metal argide ions in the plasma. In this work we performed more accurate estimations of the internal partition functions for VAr⁺ and CoAr⁺, for which the experimental measurements of molecular constants are available. The thermodynamic functions and equilibrium constant for reaction M⁺ + Ar = MAr⁺ were obtained for the temperatures up to 104 K. The molecular constants were used to construct the potential curves for the ground and excited states of the molecules. The one-dimensional Schrodinger equation was solved using the Level code to find the rovibronic levels of the electronic states for the specified potential. Different potential models such as a simple Morse potential and the potential with the long range electrostatic attraction were used for comparison. (paper)