Luminescence of 0 atoms in solid N 2 stimulated by low energy electrons

Abstract

Solid nitrogen doped with 0.1 % oxygen has been reinvestigated by using pulsed low-energy electron excitation. The resulting 0 atom emissions (ls) 2 (2s) 2 (2p) 4 β(0, 1 S - 1 D) and the associated vibrational sidebands β', β" and β'" have been examined by using a variable temperature liquid helium cryostat and photoelectric recording. This demonstrated that the electronic transition 0 ( 1 S - 1 D) is split into three zero-phonon Tines’ (z.p.l.) by the crystalline field arising at a substitutional centro-symmetric trapping site in solid N 2 . However, little or no emission arises from the z.p.l. origins since the transition is still dipole forbidden, but strong electron-phonon coupling of the three components of the 1 D state takes place and the transition becomes dipole allowed owing to asymmetric inducing low energy lattice modes. β', β" and β'" arise from the transition of O atoms simultaneous with a vibrational step down or up in the ground state of a neighbouring N 2 molecule. For β" and β'" the weak vibron-electron coupling is to symmetric non-inducing modes. Thus these transitions are shifted by the vibrational ground-state spacing energy of N 2 (X 1 Σ, v" = 6±1 to v" = 5± 1 or v" = 7±1). The initial v" = 6 + 1 value corresponds to the maximum in the intensity distribution of β" and β'" after an N 2 triplet exciton is quenched by a ground state 0 ( 3 P) atom. Since the vibron modes are non-inducing, the vibrational sidebands appear with an intensity distribution resembling the phonon induced electronic transition β.