Knowledge Bank

Here experimental tests of the selection theory for isolated strong spectral lines (Appl. Opt. 11, 2664, Nov. 1972), made with HCl gas in a 3.5 meter absorption path, are reported. At pressures between 1 and 760 torr, measured equivalent widths of sequentially pressure blended isotopic doublets are intercompared with widths predicted from published line parameters. Prior measurements of S and $\gamma$ for lines in the HCl fundamental band agree only in the upper R branch. These lines test the procedure. Resolution of the disagreement in the lower R branch and in the entire P branch --- a further purpose of this study --- is then discussed. With this long path at room temperature, absorption lines from high rotational transitions become evident at the greatest pressures. Their parameters and frequency residences are evaluated. The conformity of these observations to the assumed Lorentz profile, and thereby the validity of parameters faithful to such contours, will then be scrutinized.