Lyman and Balmer emission following core excitations in methane and ammonia molecules

Abstract

The intensities of hydrogen Lyman-α and Balmer series emission lines as a result of photoexcitation of free CH4 and NH3 molecules at the C 1s and N 1s edges have been measured. For methane, the total fluorescence yield in the visible region (300–650 nm) was also recorded. Excitation functions of the Balmer lines show relative intensity enhancement of Balmer-β emission in comparison with Balmer-α at higher core-to-Rydberg excitations. The Lyman-α emission intensity, in general, follows the relations observed in the corresponding total ion yield measurements. Additionally, the Balmer-γ and -δ yields were measured for ammonia molecules and they show intensity maxima at photon energies shifted closer to the N 1s threshold than Balmer-α and -β. A quantum defect analysis is performed to find out which core excitations are responsible for this enhanced intensity. Dissociation pathways leading to the emission in H atoms are discussed.