Following the work of Schumann (1903), the first list of vacuum ultraviolet (VUV) spectral lines emitted by an electric discharge in molecular hydrogen (H2) was published at the beginning of the century by Lyman (1904 and 1906). The spectrum was photographed at low resolution and no identification was possible at that time. Later on, Werner (1926) gave the first tentative classification of some lines. Other pioneering investigations were also performed, always at low resolution (Dieke and Hopfield, 1927; Hori, 1927; Hyman, 1930; Jeppesen, 1933). No rotational analysis was given yet in the list of characteristic band wavelengths of diatomic molecules published in 1952 by the "International Tables of Selected Constants" under the direction of Rosen (1952).

Although the absorption spectrum of H2 has been extensively studied, relatively less study was done in emission at high as well as low resolution simply because the source of light used was an ordinary glow discharge, the pressure of which (about 100 Pa) was high enough to completely prevent emission at short wavelength by radiation trapping. Regarding absorption many references before 1977 can be found in Huber and Herzberg's table (1979). The most useful are Wilkinson (1968), Namioka (1964a and b), Dabrowski and Herzberg (1974), and Takezawa (1970). The first VUV emission study of H2 at high resolution was published by Herzberg and Howe (1959), concerning the Lyman band system B¹Σ_u⁺ -> X¹Σ_g⁺, down to 118 nm. These data were used by Junkes, Salpeter, and Milazzo (1965) to list about 1500 lines of the Lyman band system that they published, together with 32 lines of the Werner band system C¹Π_u-> X¹Σ⁺_g at wavelengths longer than 113.5 nm, in an atlas of VUV atomic emission lines. Pictures of high resolution spectra were also given.

In 1980 Larzilliere, Launay, and Roncin (1980) published preliminary results about the D¹Π_u-> X¹Σ_g⁺ band system at short wavelength around 80 nm. The spectrum was obtained at Meudon Observatory with a low pressure electric discharge where self-absorption is much reduced at short wavelength. It was the first observation of emission from levels above the ionization limit. Two spectrally more extended studies were reported in 1984.The first one, by Dabrowski (1984), was devoted to the analysis of the Lyman and Werner band systems down to 100 nm. The second one, by Roncin, Launay, and Larzilliere (1984) and Larzilliere, Launay, and Roncin (1985), extended the analysis of the four unperturbed band systems C, D, D', and D''¹Π_u⁺-> X¹Σ_g⁺ down to 78 nm. At first the analysis of the very crowded emission spectrum rested on absorption data and on calculations which did not take into account the rotational coupling. However, the temperature at which the emission spectrum occurs is much higher than that for the absorption spectrum, so that the emission spectrum exhibits lines of high rotational quantum number J impossible to ascribe unambiguously except for the lowest v' (unperturbed) bands of the Lyman system and the Q branches of the ¹Π_u-> X¹Σ_g⁺ band systems.

From the theoretical point of view, Allison and Dalgarno (1970) first reported emission probabilities from each vibrational level of the B₁Σ_u+and C₁Π_u states towards all vibrational levels of the electronic ground state, neglecting the rotational coupling between B and C. In the mid-1970s, Julienne (1973) and Ford (1974 and 1975) performed the first calculations of line emission probabilities of the Lyman and Wemer band systems of H2 taking into account the rovibronic coupling between the excited states.

But at that time no complete experimental high resolution emission spectrum was available to check the calculation so that the problem was passed over. Recently several refined calculations have been performed. Abgrall et al.(1987) calculated emission probabilities for the Lyman and Werner band systems and found very good agreement with intensity measurements. The method of calculation is what we call semi-ab initio in the sense that the potential energy curves were fitted to the experimental results for each (v', J=0 or 1) before solving the system of two Schrödinger equations. An extended list of level energies and oscillator strengths has been subsequently published by Abgrall and Roueff (1989). while Senn, Quadrelli, and Dressier (1988) obtained level energies, up to J =6, of the B, B', C, and D states, calculated completely ab initio by including the four excited states in the interaction. Finally a semi-ab initio calculation, including the four excited states, has allowed Abgrall et al. (1993a, 1993b, 1993c,and 1994) to publish a complete analysis of the Lyman, Werner, B' ->X, and D->X band systems.