John H. Birely

Formation of electronically excited CO2+ in collisions of H+, H, He+, and Ne+ with CO2

Electronic excitation in collisions of 200 eV–25 keV H+, H, He+ and Ne+ with CO2 has been investigated under single‐collision conditions in an atomic beam experiment. For each of these projectiles, the B 2Σu+ and A2πu states of CO2+ are the dominant electronically excited species emitting in the 200–500 nm wavelength range owing to target excitation. Although dissociative electron capture by He+ and Ne+ to form electronically excited CO+ minimizes the energy defect, no emission is observed from CO+ A2π, and formation of CO+B2Σ+ is of only minor importance. The latter observations are in direct contradiction to predictions derived from the adiabatic criterion and demonstrate that, in the competition among allowed excitation processes, details of the electronic structure of the collision partners override energy considerations. The qualitative features of the emission spectrum excited by H+, H, and He+ are insensitive to relative velocity over the energy range covered. The ratio of the cross sections for ex...

The effect of vibrational energy on the reaction of molecular hydrogen with atomic oxygen

Abstract An upper bound of 6 × 10 10 cm 3 /moles on the rate constant for the reaction of atomic oxygen with vibrationally excited H 2 has been deduced from laboratory observations and from detailed computer calculations. From this result it can be shown that no more than 30% of the vibrational energy of H 2 is effective in overcoming the activation energy for the O + H 2 reaction.

Electronic excitation in collisions of fast protons and hydrogen atoms with NO, N2O, CO2, and OCS

Analyses of radiation in the 115–850 nm range produced by collisions of 10–25 keV H+ and H with NO, N2O, CO2, and OCS under thin target conditions have been carried out. In agreement with our earlier observations for CO2, the most prominent features for the polyatomic targets are emitted by excited parent molecule ions. Except in the case of OCS, for which weak CO+ (B 2Σ+–X 2Σ+) bands were detected, the cross sections for dissociative excitation to yield diatomic fragments are extremely small. These observations in conjunction with results obtained elsewhere for other projectile ions provide further evidence that in the competition among allowed excitation channels, details of the electronic structure of the collision partners override energy considerations. For an NO target, the NO+ (A 1Π–X 1Σ+) bands are observed, and, for all of the molecules studied, atomic lines owing to dissociative excitation are prominent in the spectra.

Lyman‐Alpha Emission Cross Sections for Collisions of 1–25 keV H+ and H with CO, CO2, CH4, and NH3

Cross sections are reported for emission of Lyman‐α radiation in collisions of H+ and H with CO and CO2 in the 1–25‐keV energy range and with CH4 and NH3 in the range 5–25 keV. In the experiments with CH4 and NH3 the Doppler‐shifted Lyman α, emitted by H(2p) formed in electron capture by fast incident protons or collisional excitation of fast incoming hydrogen atoms, and the virtually unshifted Lyman α, emitted by the far slower H(2p) produced in dissociative excitation, were separated. An electric field was applied within the collision chamber, and the increase in Lyman‐α intensity was used to derive cross sections for formation of H(2s). For CO and CO2 targets, H projectiles are more efficient than H+ in formation of H(2p), while at energies above 10 keV, H+ is more efficient than H in formation of H(2s). For both projectiles, the probability of formation of H(2p) is greater than or equal to the probability of forming H(2s). For CH4 and NH3 targets the projectile excitation cross sections are generally ...