Luminescence of Nitrogen and Oxygen Atoms in Solid Nitrogen, Neon, Argon, Nitrogen/neon and Nitrogen/argon Stimulated by Low-Energy Electrons.
Abstract
The spectral characteristics of the (alpha)(N('2)D -('4)S) and (beta)(O('1)S-('1)D) emissions, within the ground state configurations of nitrogen and oxygen atoms, trapped in solid nitrogen, neon, argon, N(,2)/Ne and N(,2)/Ar, have been investigated in order to determine (1) the matrix perturbations upon the gas phase transitions of the free atoms; (2) the structure of the guest-active states in the forbidden energy gap region between the phonon and exciton bands of the pure solids and (3) to construct an overall picture of the macroscopic solid from a detailed understanding of the microscopic nature of the various trapping sites. A variable temperature liquid helium cryostat was used to maintain a nickel plated target at temperatures between 4.2K and 30.0K. Research grade gases were mixed to the desired ratios and then deposited onto this cold substrate. Upon bombarding these films with low energy electons (< 500 ev), N and O atoms were produced "in situ" by the dissociation of the precursor molecules N(,2) and O(,2) and trapped in small concentrations. The electron gun, cold target and gas deposition nozzle were located inside a high vacuum chamber. The light emitted from these solids was analyzed by means of visible spectroscopic techniques employing photoelectric recording. The radius directus proceeded along experimental lines calling to aid when necessary the following specific techniques. Spectral intensity distributions were recorded at a variety of excitation energies and at a number of different temperatures. Effect of annealing were noted. Decay curves of individual features and afterglow spectra for long lived transitions were also recorded. Experiments were conducted using films composed of layers of different matrix materials or by continuously depositing new matrix material during excitation. Binary solids were produced by purposely introducing small amounts of impurities into solid N(,2), Ne or Ar and by diluting pure N(,2) with large amounts of Ne or Ar. In solid nitrogen the components comprising the (alpha)(N('2)D-('4)S) emission arise from dipole radiation, induced by static and dynamic fields, from N atoms in at least five different sites within the matrix. In solid nitrogen doped with 0.1% O(,2), the (beta) group is composed of three broad components arising from the splitting of the electronic transition (('1)S-('1)D), of O atoms trapped in one characteristic site, coupling to inducing phonon modes. Unlike the vibron-electron coupled structure (alpha)'', (alpha)' or (alpha)''', which reflect the ground state vibrational level structure of a neighboring N(,2) molecule, (beta)'', (beta)' and (beta)''', reflect the splitting and intensity distribution of the electronic transition (beta). In solid neon doped with a total of 0.1% X where X is N(,2), O(,2), CO, Ar or a combination of these species, individual components in the spectrum of (alpha)(N('2)D -('4)S) and (beta)(O('1)S-('1)D) appear to arise from impurity -affected sites as well as "pure" sites in which the N or O atom replaces a Ne atom and the dynamic interatomic field, which may include impurity-activated modes, induces the transition. N(,2)/Ne alloys form two types of binary solids. A monophase amorphous solid characterized by a well-mixed but non-structured matrix and a phase separated solid. N(,2)/Ar mixtures solidify as monophase binary solids over the concentration range from pure N(,2) to 0.01% N(,2)/Ar. Upon dilution of N(,2) with Ar the influence of the most abundant host can be followed in the spectral structure of (beta)(O('1)S-('1)D) but not (alpha)(N('2)D -('4)S). The high temperature dynamically induced structure of (alpha), which arises from N atoms in substitutional but non-centrosymmetric sites, shows little sensitivity to a concentration change of from about 33% Ar/N(,2) to 99% Ar/N(,2). The low temperature structure of (alpha) is complex being comprised of at least five separate components. As the rare gas host atom gets larger (Ne, Ar, Kr, Xe), both the (alpha)(N('2)D-('4)S) and (beta)(O('1)S -('1)D) transition energies continuously shift towards lower energies, solid neon providing the most gas-like medium.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1980
- Bibcode:
- 1980PhDT.......201S
- Keywords:
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- Physics: Condensed Matter