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Zero field level crossing in molecular hydrogen Van der Linde, Jacob

Abstract

The lifetimes of the 3d¹Σ(v=0) J = l, 2 and 3 states have been measured using zero-field level crossing techniques. The transitions observed were the R-branch members of the 3d¹Σ ↦ 2p¹Σ transition. The upper state is excited in a discharge between two capacitor plates to which a radio-frequency voltage is applied. The measurements were made using first a 180 MHz R.F. source and later using a 450 MHz source. Polarization of emitted light was measured by rotating a polaroid in the beam and phase sensitive detecting the resulting modulation. The depolarization curves obtained by plotting the magnetic field strength against the polarization of the R(0), R(l), R(2) lines yield halfwidths, when extrapolated to zero pressure, of 2.37±.12 gauss, 2.60±.15 gauss and 3.25±.25 gauss. The halfwidths vary linearly with pressure in the discharge cell yielding collision cross-sections of roughly 1.5x10⁻¹⁴ cm². Using the high field Landé g values of these states, their lifetimes are (2.66±.12)x10⁻⁸sec., (3.83±.2)x10⁻⁸sec., and (3.93±.25)x10⁻⁸sec. for J=l, 2 and 3 respectively. The discrepancy between the first and the latter two lifetimes is discussed.

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