High‐Resolution Electron‐Impact Emission Spectrum of H 2 . I. Cross Sections and Emission Yields 900–1200 A

Abstract

High-resolution (Δλ = 115 mÅ) emission spectra of molecular hydrogen produced by electron-impact excitation at 100 eV have been obtained in the wavelength range 900-1200 Å. The emission spectra can be assigned to transitions between the X 1Σg+ ground state and the 1sσgnpσu1Σu and 1sσgnpπu1Πu Rydberg states. Synthetic rotational line spectra based on the excitation function of Liu et al. and calculated 2pσ B 1Σu+-X 1Σg+, 2pπ C 1Πu-X 1Σg+, 3pσ B′ 1Σu+-X 1Σg+, and 3pπD 1Πu-X 1Σg+ transition probabilities of Abgrall et al. are generally found to be in good agreement with the experimental spectra in the regions where emissions from 1sσg npσu (n ≥ 4) and 1sσg npπu (n ≥ 4) states are negligible. Emission cross sections for D 1Π+u, D′ 1Πu, and D″ 1Π-u, B′ 1Σu+, and B″ 1Σu+ states are obtained by measuring the emission intensities from these states relative to those from the B 1Σu+,C 1Πu, and D 1Π-u states. A high-resolution EUV calibration technique is established. At 100 eV the emission cross sections of the D 1Πu, D′ 1Πu, D″ 1Πu, B′ 1Σu+, and B″ 1Σu+ states are measured to be (2.8 ± 0.4) × 10-18, (6.3 ± 1.3) × 10-19, (5.9 ± 1.7) × 10-20, (2.1 ± 0.3) × 10-18, and (1.6 ± 0.4) × 10-19 cm2, respectively. In addition, the vibrational emission cross sections have been compared to the estimated excitation cross sections to obtain the predissociation yields for selected vibrational levels of the D 1Π+u, D′ 1Π+u and D″ 1Π+u states. The B′ 1Σu+ state is inferred to have very significant excitation into the H(1s)+H(2p, 2s) dissociative continuum.