The electron-excited mid-ultraviolet to near-infrared spectrum of H2:: Cross sections and transition probabilities

At high resolving power (lambda/Delta lambda approximate to 10; 000), we have measured the electron impactYinduced fluorescence spectrum of H-2 from 3300-10000 angstrom 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 (EF (1)Sigma(+)(g), GK (1)Sigma(+)(g), H (H) over bar (1)Sigma(+)(g), I-1 Pi(g), J(1)Delta(g)...-> B-1 Sigma(+)(u), C-1 Pi(u), B'(1)Sigma(+)(u), D-1 Pi(u)) and the Rydberg series of triplet states dominated by d(3)Pi(u), k(3)Pi(u), j(3)Delta(g) -> a(3)Sigma(g)' band systems. A model VOIR spectrum of H-2 from 7500 to 10000 angstrom, 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) cm(2); the excitation cross section to the triplet states at 20 eV was found to be (1: 38 +/- 0: 41); 10(-18) cm(2). 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 H-2 (a(3)Sigma(+)(g)-b(3)Sigma(+)(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 angstrom.