The Electron-Excited Mid-Ultraviolet to Near-Infrared Spectrum of H2: Cross Sections and Transition Probabilities

International audienceAt high resolving power (lambda/Deltalambda~10,000), we have measured the electron impact-induced fluorescence spectrum of H2 from 3300-10000 Å at 20 and 100 eV. We have analyzed the visible-optical-near-IR (VOIR) emission spectrum under optically thin, single-scattering experimental conditions. The high-resolution spectrum contains transitions from the gerade Rydberg series of singlet states to the ungerade series of Rydberg states (EF1Sigma+g, GK1Sigma+g, HH¯1Sigma+g, I1Pig, J1Deltag...-->B1Sigma+u, C1Piu, B'1Sigma+u, D1Piu) and the Rydberg series of triplet states dominated by d3Piu, k3Piu, j3Deltag-->a3Sigma+g band systems. A model VOIR spectrum of H2 from 7500 to 10000 Å, based on newly calculated transition probabilities and line positions including rovibrational coupling for singlet gerade states, is in excellent agreement with the observed intensities. The rotational line emission cross sections for direct excitation of the singlet states at 100 eV and triplet states at 20 eV were measured. The absolute cross section values for excitation to the singlet gerade states at 100 eV was measured to be (4.58+/-1.37)×10-18 cm2; the excitation cross section to the triplet states at 20 eV was found to be (1.38+/-0.41)×10-18 cm2. The singlet gerade emission cross sections are the cascading cross sections to the UV spectrum (including the Lyman and Werner band systems) and the triplet state emission cross sections are the cascade dissociation cross sections of the H2 (a3Sigma+g-b3Sigma+u) continuum for the production of fast hydrogen atoms. Electrons are also effective in exciting high vibrational levels belonging to ungerade symmetry (B, B', C, D) which subsequently emit toward gerade symmetry states in the VOIR domain. Strong emission from the ungerade-gerade transitions are observed from 7300 to 7400 Å