Collision broadening and shifts in the spectra of neutral and singly ionised calcium

Abstract

Measurements are reported of the broadening and shifts, due to collision with helium and argon, of the neutral calcium line 4227 AA and the Ca+ resonance lines 3968 and 3933 AA (the solar H and K lines) and the associated lines 8542 and 8662 AA. The lines are obtained in emission from a flow lamp and the profiles recorded from a scanning Fabry-Perot interferometer are analysed numerically. The very nearly equal broadenings of the H and K lines and the corresponding infrared lines indicate that the broadening in both multiplets is essentially determined by the common upper configuration. The observed broadening is between 1.3 and 2 times the predictions of van der Waals theory. Comparison with high-temperature shock-tube measurements indicate that the broadening varies as T0.4+or-0.02 for helium and T0.25+or-0.07 for argon.