Density-dependent frequency shift of the hydrogen S2/1/ quadrupole line

An optical parametric oscillator pumped with an Nd:YAG laser was used in the investigations along with a White cell and a scanning spectrometer. The frequency of the S2(1) line was measured at a temperature of about 293 K over the density range from 1 to 4.3 amagat with the aid of a technique reported by Douglas and Sharma (1953). It was found that the obtained data are in good agreement with measurements conducted by Fink et al. (1965).