### Collisional Excitation and Ionization at Shocks

Cross sections and rate coefficients for collisional excitation and ionization
of hydrogen plotted as a function of energy (adapted from Janev etal 1987).
The solid and dot-dashed curves (< sigma v_1i >, where i = 2, 3, infinity)
show the rate coefficients for collisional excitation and ionization for n = 1 -> i
by thermal electrons at temperature T = E/k.
The dashed and dotted curves are cross sections and use the ordinate at right.
For shock velocities of interest 30 -- 300 km/s;
1.8 - 180 eV the cross sections for collisional excitation are comparable to the
cross section for collisional ionization. Collisional excitation and ionization by protons and
charge exchange to excited states become important (more than a 10% correction to < sigma v >)
when E> 1000 eV.
Published in Hartigan, P. 1997, HST Observations of the HH 47 and HH 111 Stellar Jets ,
in ``Accretion Phenomena and Related Outflows'', IAU Colloquium 163,
ASP Conference Series Vol. 121, D. T. Wickramasinghe, G. V. Bicknell, & L.
Ferrario eds., p536.