Lyman-α Fluorescence from the Photodissociation of H2

Abstract

Photodissociation and fluorescence cross sections for H2 have been measured from 860 to 700 Å by observing the Lyman-α photons emitted at 90° to an incident photon beam. The photodissociation quantum efficiency was found to be unity from 850 Å to the photoionization threshold at 804 Å and about 10% at shorter wavelengths. By observing the fluorescence radiation as a function of decreasing pressure, it was determined that most of the excited H atoms were formed in the metastable 2s state and that the Lyman-α emission results primarily from collisional quenching. The ratio of the collisional cross section with and without Lyman-α emission was measured for different relative velocities and was found to increase appreciably with increasing velocity.