Knowledge Bank

A tunable laser was used in combination with a 25-m base-path White cell and a 5-m spectrometer to obtain measurements of the equivalent width and frequency of the $S2$(l) line of hydrogen over the density range of one to four amagat. The long optical path permits ratioing (I/I$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}$) to be done with a single detector. The equivalent widths analyzed in terms of a Galatry line shape yield a line strength in excellent agreement with the ab initio calculations. The pressure shift of the $S2$(l) frequency is approximately twice that measured for the $S1$(l) line. This result indicates a perturbation of the vibrational force constant and is consistent with results obtained with hydrogen $deuteride.1,2$