A Experimental Study of the Vibrational-Rotational Spectrum of Molecular Hydrogen.

The quadrupole spectrum of molecular hydrogen has been measured in the 1-0 through 4-0 vibrational-rotational bands. In each band the shapes of the hydrogen lines have been analyzed using the Galatry function. In addition, spectral features, termed 'dips' have been analyzed in the fundamental band of the pressure induced dipole spectrum. Observations were made with the Fourier Transform Spectrometer at the McMath Solar Telescope of the Kitt Peak National Observatory. This instrument permitted spectra to be obtained with high resolution and large signal-to -noise ratios. Observations were made over a range of pressures between 0.8 and 2.85 atmospheres. The Galatry function was fit to each of the quadrupole lines. The 'dips' in the induced dipole were simultaneously fit with a dispersion profile. Several new effects are reported as well as improvements over previous measurements for this molecule. Accurate quadrupole line positions in the 1-0 band in many rotational levels permitted the recalculation of the ground state rotational constants. The values of the rotational constants thus determined are (in cm('-1)) B = 59.33451, D = 0.045651 and H = 4.56 x 10('-5). The values of the pressure broadening coefficient as determined by the Galatry function, indicate a new effect. The pressure broadening coefficients are directly proportional to the vibrational quantum number. The pressure broadening coefficient at high vibrational levels is therefore much larger than previously thought. The 'dip' in the pressure induced dipole spectrum has been observed in the 1-0 band. Such 'dips' are the spectral features produced by intercollisional interference in the pressure induced dipole. The 'dips' appear superimposed upon the allowed quadrupole transitions. 'Dips' are observed at both the Q branch and S branch lines in pure hydrogen. The profile of the 'dip' has been fully resolved and analyzed. Analysis indicates that the 'dips', contrary to current theories, are not symmetric features. In addition, a new spectral feature has been observed for the S branch lines only. This feature is an increase in the absorption, as opposed to the 'dips' which are a decrease in the absorption. This new spectral feature is described, and possible origins of the feature are discussed.