Emission cross section measurements in protron nitrogen collisions using photon coincidence techniques

Abstract

The measurement of a cross section for the emission of a Balmer alpha (6563A) and N⁺₂ (0,0) first negative band (3914A) photon from a hydrogen atom and an N⁺₂ molecule which are excited simultaneously in the same H⁺+N₂ charge exchange collision has been performed in the proton velocity range from .54x10⁸ cm/sec (1.5 keV) to 2.40x10⁸ cm/sec (30.2 keV). The measurement has been accomplished using the technique of proton-photon coincidence detection. Details of the technique are presented. The simultaneous specification of the emissions (and hence final state excitations) of both systems produced in the collision makes this first measurement of an emission cross section for a "well specified" charge exchange reaction. The specific cross section measured is that for the emissions resulting from simultaneous excitation of the B²Σ⁺u, v¹=0 state of N⁺₂ and the 3p or 3d state of hydrogen. To within the random error associated with the experiment, the cross section has only a single-peak structure with a maximum value of ~1.2x10⁻¹⁸ cm² at a velocity of 1.15x10⁸ cm.sec (6.9 keV). The primary significant result of the investigation is the exceptionally good agreement in both shape and magnitude between the measured cross section and the cross section, σuc, calculated on the assumption that the final state excitation of the two product systems are independent events. The average value of the ratio of the measured cross section to σuc for the twelve measured values of the cross section is 1.11+.34. Secondary results are the measurement of the total cross section for the production of 3914A emission in H⁺+N₂ collisions showing good agreement with previous measurements and the redetermination of the total cross section for the production of Balmer alpha emission in the same type collisions showing varying degrees of agreement with previous measurements.