Abstract: The emission spectrum of microwave-driven sulfur lamp was obtained by experimental measurement. The emission moment of S₂ B³Σ_u^-X³Σ_g^- and B″³Π_u-X³Σ_g^- electronic states and the Franck-Condon factors between their vibrational level were calculated by quantum ab initio method of multi-configuration quasi-degenerate perturbation theory and cc-pVQZ basic set, then, their emission spectra were derived. Absorption spectra of S_n(n=2—8) molecules were also calculated via time-dependent density functional theory. The emission spectrum and experimental one of S₂ molecules were took step to compare and analyze. The results can be used to well explain the emission spectrum characteristic of the microwave-driven sulfur lamp. The theoretical simulation results can well guide the further experiments to fit better with sun′s spectrum.

Key words: Multi-configuration quasi-degenerate perturbation theory, Time dependent density functional theory, Franck-Condon factor, Emission spectrum of S₂ molecule