Excitation Transfer from Ar~* to H_2 in a Gas-Discharge Plasma

摘要

Spectral distributions of the emission intensity over a range of 200-400 nm, where the dissociation continuum (a~3Σ_g~+ → b~3Σ_u~+) of a hydrogen molecule is located, are measured in a hollow-cathode glow-discharge plasma of mixtures of hydrogen with argon, neon, and krypton at pressures of 0.8 to 10 torr. The continuum shape is found to be substantially dependent on the ratio of constituents of the Ar-H_2 mixture. Within the limits of experimental accuracy, the shape of the continuum of a mixture of hydrogen with neon and krypton is the same as that of pure hydrogen. The experiments carried out with the active phase and afterglow of the discharge demonstrated that a change in the continuum shape in the presence of argon results from the excitation transfer from long-lived excited states of argon atoms to H_2 molecules. Possible excitation transfer mechanisms are analyzed. It is shown that, if energy considerations are used, the rotational and translational energies of an H_2 molecule should be taken into account.