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

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 1 Σ ground state and the 1 s σ g np σ u 1 Σ u and 1 s σ g np π u 1 Π u Rydberg states. Synthetic rotational line spectra based on the excitation function of Liu et al. and calculated 2 p σ B 1 Σ - X 1 Σ , 2 p π C 1 Π u - X 1 Σ , 3 p σ B ' 1 Σ - X 1 Σ , and 3 p π D 1 Π u - X 1 Σ transition probabilities of Abgrall et al. are generally found to be in good agreement with the experimental spectra in the regions where emissions from 1 s σ g np σ u ( n ≥ 4) and 1 s σ g np π u ( n ≥ 4) states are negligible. Emission cross sections for D 1 Π , D ' 1 Π u , and D '' 1 Π , B ' 1 Σ , and B '' 1 Σ states are obtained by measuring the emission intensities from these states relative to those from the B 1 Σ , C 1 Π u , and D 1 Π states. A high- resolution EUV calibration technique is established. At 100 eV the emission cross sections of the D 1 Π u , D ' 1 Π u , D '' 1 Π u , B ' 1 Σ , and B '' 1 Σ 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 cm 2 , 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 1 Π , D ' 1 Π and D '' 1 Π states. The B ' 1 Σ state is inferred to have very significant excitation into the H(1 s )+H(2 p ,2 s ) dissociative continuum.