Laboratory studies of ionization and excitation of atmospheric gases in collisions with 0.1- to 1000-kev protons and hydrogen atoms are reviewed. Recent measurements of the mixed flux of H+ and H that penetrates the auroral zone atmosphere during a hydrogen aurora indicate that particles with energies less than 10 kev are most important, which implies that energetic hydrogen atoms cause most of the observed ionization and light emission. Both H+ and H produce free electrons by collisional ionization of atmospheric constituents, and stripping of energetic H is an additional source of electrons. Reliable data are available for the cross section for production of electrons in collisions of H+ and H with all important target gases, except atomic oxygen, over the full range of auroral energies. Excitation of atmospheric gases has been widely studied for H+ collisions in the range above 10 kev, but cross sections for H+ below 10 kev and H in any energy range are still largely unknown. Data are available for calculation of expected auroral emissions in the υ′ = 0 bands of the N2+ first negative system and in the υ′ = 0 bands of the N2 second positive system. The ratio of the cross section for electron production by ionization to the cross section for emission of the 391.4-nm band of the N2+ first negative system is found to be about 20 for energies above 10 kev and then to rise to more than 100 at 1 kev. In the case of the hydrogen emissions, laboratory data are adequate for auroral calculations of Lyman α radiation. Collisional excitation of energetic H to the 2p level, rather than charge transfer excitation involving fast H+, is the major source of Lyman α in the hydrogen aurora. Data on the production of the Balmer α line are lacking at energies below 10 kev. The available Balmer α data suggest a broad peak near 10 kev in the effective auroral cross section that is nearly an order of magnitude smaller than the peak in the Lyman α cross section, which occurs at energies less than or equal to 1 kev. Insufficient laboratory data exist for meaningful calculations of auroral Hβ intensities.

Laboratory studies of collisions of energetic H+ and hydrogen with atmospheric constituents

This report describes the development of the theory of charge exchange in collisions of ions with atoms or ions, paying particular attention to the work of the last decade. The successful approximations based on the impact parameter and classical path methods, suitable for low energy collisions, are treated in detail. For high energies, approximations that are completely satisfactory from a theoretical viewpoint do not exist, but both the Born approximation and the classical models of Gryzinski and Thomas are found empirically to reproduce many features of the observed cross sections and a discussion is given of the successes and limitations of these and related models. This review was completed in March 1972.

The theory of charge exchange

Motivated by proton auroral studies, we extend the microscopic approach developed for electrons, which is based on detailed collisional cross sections, to deal with the problem of proton energy deposition in N2. Our calculated excitation efficiencies, which include the contributions from charge exchange processes and secondary electrons, remain fairly constant from 1 kev to 10 Mev for the ionization states but vary considerably below 10 kev for excitation states and dissociation processes due to charge exchange effects. The estimates of the Lyman α and Hα photon production are found to be very sensitive to the low-energy hydrogen impact cross section. The Lyman α and Hα photon production tends to be higher than previous estimates of Eather. Good agreement with the results of Chubb and Hicks is obtained for the Lyman α/Lyman-Birge-Hopfield intensity ratio. Total intensities for a typical proton auroral energy of 4 kev and a polar glow aurora of 1 Mev are presented.

Energy deposition of protons in molecular nitrogen and applications to proton auroral phenomena

Capture of an electron into the continuum of a fast proton is studied by measuring the energy spectra of the emitted electrons at zero emission angle relative to the direction of the incident proton beam. The data include doubly differential cross sections as well as peak yields for 15 to 1500 keV impact energies and targets of He, Ne, Ar and H2 under single-collision conditions.

https://iopscience.iop.org/article/10.1088/0022-3700/12/17/017/pdf

Charge transfer to the continuum for 15 to 1500 keV H+ in He, Ne, Ar and H2 gases under single-collision conditions

The continuum distorted-wave (CDW) approximation is used to calculate total cross sections for the charge-exchange process H++He(1s2) to H(1s, 2s, 2p, 3s, 3p, 3d, 4s)+He+(1s) in the impact energy range 25 keV-10.5 MeV. The results obtained are compared with experimental data and it is found that the CDW method is quite successful in the prediction of the electron capture into the s states of H. The CDW cross sections Qtot for the electron capture summed over all final projectile bound states in the reaction He2++He(1s2) to He+( Sigma )+He+(1s) agree well with experimental data at impact energies 500 keV-7 MeV. In addition, several approximate good-state wavefunctions of He are used to establish the degree of sensitivity of the CDW cross sections to the choice of wavefunction.

Charge exchange in fast collisions of H+ and He2+ with helium

Absolute cross sections for electron capture into the $3p$ and $3d$ states of hydrogen have been measured for 10- to 100-keV proton impact on He, Ne, Ar, ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and ${\mathrm{O}}_{2}$. Improved $3s$ cross sections are presented for these gases from 10 to 120 keV. An apparent maximum in the $3p$ cross section occurs in this energy range for all gases. The $3d$ cross sections decrease monotonically with increasing impact energy according to an $\mathrm{exp}[\ensuremath{-}{(\frac{E}{K})}^{\frac{1}{2}}]$ relationship, where $E$ is the impact energy and $K$ is a constant, with the exception of helium which shows a maximum in the $3d$ cross section between 15 and 20 keV. The value of $K$ is identical for all the diatomic gases. Balmer-$\ensuremath{\alpha}$ cross sections are synthesized from these results. Polarization of the $3d\ensuremath{\rightarrow}2p$ radiation is reported.

Electron Capture into the n = 3 States of H by Fast H + Impact on Gases

PRODUCTION OF H ATOMS IN THE 3s STATE BY THE DISSOCIATION OF FAST H$sub 2$$sup +$ AND H$sub 3$$sup +$ PROJECTILES ON IMPACT WITH H$sub 2$, He, Ar, AND Ne.

E. D. Stokes

Papers

Electron Capture into the n = 3 States of H by Fast H + Impact on Gases

PRODUCTION OF H ATOMS IN THE 3s STATE BY THE DISSOCIATION OF FAST H$sub 2$$sup +$ AND H$sub 3$$sup +$ PROJECTILES ON IMPACT WITH H$sub 2$, He, Ar, AND Ne.

Some Total Electron‐Capture Cross Sections for H2+ and H3+ Impact on Ne, and H3+ on Ar