Measurement of the broadening and shift of the Na D lines by helium at low pressure

Abstract

The broadening and shift of the Na D₁ and D₂ lines have been measured at 450 K with a dual beam Fabry-Perot spectrometer system. The pressure was kept below 100 Torr and the hyperfine structure of the lines was resolved. In units of 10^-9 rad s^-1 cm³, the shift is found to be less than 0.05 and ( gamma /N)_D1=1.52+or-0.1, ( gamma /N)_D2=1.62+or-0.1. These results are compared with the values obtained by an elaborate theoretical treatment which takes into account the anisotropy of the interaction potential and the non adiabatic effects due to rotational coupling. Excellent agreement is found between experimental and theoretical results. The validity of various simplified theoretical treatments is also examined.