1. Introduction

The interactions among electrons, ions, and hydrogen atoms are the most important processes which occur in laboratory and astrophysical plasmas. The understanding of these collision processes is essential for diagnosing and modeling plasmas in controlled fusion experiments, plasmas processing, and astrophysics. In addition to the application of studying plasma dynamics, collision processes such as electron-impact excitation, ionization, and charge exchange processes are interesting from the view of fundamental physics, like many-body collision dynamics.

In this paper, we focus attention on carbon atoms and ions C^q+ (q = 0–6). Carbon atoms and ions are abundant in various astrophysical environments, fusion reactors, and plasma-chemistry atmospheres. We consider electron-impact excitation and ionization of these atoms and ions, as well as charge exchange processes in collisions between carbon ions and hydrogen atoms. Therefore, we have collected the data for cross sections from the literature and have critically assessed their accuracy to obtain recommended data. The recommended data have been fitted to simple analytical fit functions. For electron-impact excitation processes, rate coefficients have also been derived. The fit coefficients are presented in the tables. The values derived from fitted functions are presented as the recommended data in the graphs, together with the original data from the literature. We have taken into account the important transitions for excitation, ionization, and charge exchange processes. For these data and the processes which are not shown in this paper, the original data can be found at NIFS Database webpage http://dbshino.nifs.ac.jp: AMDIS for excitation and ionization, and CHART for charge transfer (charge exchange).

This paper is organized as follows. First, we deal with electron-impact excitation of C^q+ (q = 0–5) atoms and ions. Second, electron-impact ionization processes of these atoms and ions are considered. The double-ionization of C⁺ is also presented. Next, charge exchange cross sections between carbon ions C^q+ (q = 1–6) and hydrogen atoms are presented, including state-selective cross sections. Finally, a brief summary of the work is given.

1.1. Electron-impact excitation of carbon ions and atoms

There are numerous theoretical cross section data for electron-impact excitation of carbon ions. Previously, Itikawa et al. [1] compiled cross sections reported until 1985 for carbon ions (C⁺–C⁵⁺) as well as oxygen ions (O⁺–O¹²⁺), critically evaluated the data, and fitted the recommended values to analytical formulae. Before 1985, cross sections were calculated by the distorted-wave method, the Coulomb–Born approximation, the Coulomb–Born Oppenheimer method, and the close-coupling method. These are reported for various excitation processes of all ions C⁺–C⁵⁺ in Los Alamos Scientific Reports (1977) [2], [3], [4] and [5]. McDowell et al. [6] had calculated electron-impact excitation cross sections for C⁵⁺ and C⁴⁺ ions using the distorted-wave method. Close-coupling calculations had been carried out for C⁴⁺ by Foster et al. [7]. Berrington et al. [8] and [9] had reported cross sections calculated by the R-matrix method. In the following, we have compiled cross section and rate coefficient data for electron-impact excitation of carbon atoms and ions reported after 1985 and have given the recommended data. These recommended data are fitted to analytical functions. The references for the data which we adopted as recommended data are shown in Table 1, Table 2, Table 3, Table 4, Table 5 and Table 6.