Ionization

Full text: The partial and total ionization cross section for the ground state neutral N2 molecule by the impact of electron has been studied extensively by Itikawa, Lindsay and Mangan and Tabata et al in their reviews. These reviews are based on the experimental work of Straub et al, Rapp and Englander-Golden, Tian and Vidal Hudson et al and Krishnakumar and Srivastava. Among all the reviews, Itikawa has done the most comprehensive work on N2 molecule, surveying literature till the end of 2003. After going through previous reviews, evaluating existing data and deliberations through discussions, it was accepted during the meeting that the measurements of Straub et al will be adopted as the recommended data set for partial (N2+, N+ and N2+) and total ionization cross section. Straub et al have used a time-of-flight mass spectrometer to detect product ions within an uncertainty of 3.5%. However, below 25 eV, the data reported by Straub et al is fragmentary and hence, the mean of Straub et al and Rapp and Englander-Golden are considered in this energy range as they gives very good agreement with Straub et al. Above 50 eV, the data reported by Rapp and Englander-Golden is slightly on the higher side of the recommended data. Rapp and Englander-Golden reports an uncertainty of 7% in their measurement. However, the overall uncertainties estimated are 5% for the production of N2+ and N+ ions and 6% for the N++ ion. It is to be noted that N+ may also include N2++, as measurements cannot resolve same-charge-to-mass ratio fragments. However, a rough estimate by the authors shows that the contribution may me quite small (< 0.5%) and hence can be neglected. For the production of other fragments like N+ + N, N2+ + N and N+ + N2+ the data reported by Tian and Vidal with an uncertainty of 10% was recommended. The recommended data set for the total ionization cross section was obtained by adding all the individual partial ionization cross sections with an estimated uncertainty of 5%. Besides the works reported above, various other experimental and theoretical data also exist in the literature. Krishnakumar and Srivastava (with 10% uncertainty) and Hudson et al (with 5% uncertainty) have also measured total ionization cross section of N2 by electron impact. Toth et al, Hwang et al and Joshipura et al have calculated total ionization cross section of e-N2 using distorted wave Born approximation (DWBA), binary-encounter-bethe (BEB) and complex scattering potential-ionization contribution (CSP-ic) methods respectively. In general, all these data agrees reasonably well with the recommended data. (author)