Rydberg and charge-transfer states of atomic oxygen in Ar and Kr matrices: identification of two distinct sites

Photolysis of O2 dispersed in solid neon with far-ultraviolet radiation

Irradiation at 173 or 143 nm of samples of ¹⁶O₂ or ¹⁸O₂ in solid Ne near 4 K produced many new spectral lines in absorption and emission from the mid-infrared to the near-ultraviolet regions. The major product was ozone, O₃, that was identified with its mid-infrared and near-ultraviolet absorption lines. Oxygen atoms were formed on photolysis of O₂ and stored in solid neon until the temperature of a sample was increased to 9 K, which enabled their migration and combination to form O₃ and likely also O₂. O₂ in five excited states and O in two excited states detected through the emission spectra indicate that complicated processes occurred in solid Ne after far-ultraviolet excitation. For the transition ¹D₂ → ³P_1,2 of O, the lifetime was determined to be 5.87 ± 0.10 s; the lifetime of the upper state of an unidentified transition associated with an emission feature at 701.7 nm was determined to be 2.34 ± 0.07 s.

Thresholds of photolysis of O2 and of formation of O3 from O2 dispersed in solid neon

Irradiation of O₂ dispersed in solid Ne with light of wavelength less than 200 nm produced O, O₂ and O₃.

Charging effects in an electron bombarded Ar matrix and the role of chemiluminescence-driven relaxation

The relaxation processes in pure and doped Ar films preirradiated by an electron beam are studied with the focus on charging effects. Correlated real time measurements have been performed applying current and optical activation spectroscopy methods. Thermally stimulated exoelectron emission and thermally stimulated luminescence are detected in the vacuum ultraviolet and visible range. An appreciable accumulation of electrons in the matrix is found, and prerequisites for negative space charge formation are ascertained. The part played by pre-existing and radiation-induced defects as well as dopants is considered and the temperature range of the electron trap stability is elucidated. It is shown that laser-induced electron detachment from O(-) centers results in an enhancement of electron detrapping via the chemiluminescence mechanism, viz. neutralized and thermally mobilized O atoms recombine. Formation of O(2)* results in the emission of visible photons. These photons act as a stimulating factor for electron release and transport, terminating in exoelectron emission and charge recombination. Chemiluminescence therefore plays an important role in the decay of charged centers.

Formation of HXeO in a xenon matrix: Indirect evidence of production, trapping, and mobility of XeO (1 1Σ+) in solid Xe

IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 30 K. Irradiation at 240 nm after the photolysis at 193 nm depletes the oxygen atom emission at 750 nm and reduces the amount of HXeO generated in subsequent annealing. Part of the 750 nm emission can be regenerated by 266 nm and this process increases the yield of HXeO in annealing as well. Thus, we connect oxygen atoms emitting at 750 nm with annealing-induced formation of HXeO radicals. Ab initio calculations at the CCSD(T)/cc-pV5Z level show that XeO (1(1)Sigma(+)) is much more deeply bound [D(e) = 1.62 eV for XeO --> Xe+O((1)D)] than previous calculations have predicted. Taking into account the interactions with the medium in an approximate way, it is estimated that XeO (1(1)Sigma(+)) has a similar energy in solid xenon as compared with interstitially trapped O((3)P) suggesting that both possibly coexist in a low temperature solid. Taking into account the computational results and the behavior of HXeO and O(3) in annealing and irradiations, it is suggested that HXeO may be formed from singlet oxygen atoms which are trapped in a solid as XeO (1(1)Sigma(+)).

Concentration dependence of the spectroscopic and photochemical properties of atomic and molecular oxygen in argon matrices

Vacuum ultraviolet (VUV) excitation (200-100 nm) and visible emission (300-650 nm) spectra of O2 imbedded in Ar matrices at different concentrations are presented. At 0.1 and 0.2% concentrations a linear increase in the intensities of the excitation and emission spectra is observed. At these concentrations, photolysis of O2 is found to be negligible. At higher concentrations (0.5, 1 and 2%) the normalized intensities of the excitation and emission spectra of O2 decrease. With increasing concentration of O2 the permanent photolysis of O2 increases, which does not correlate, based on the excitation spectra of O in Ar, to the production of isolated O atoms. It has been shown that this anomalous behavior should be due to the formation of van der Waals dimers and oligomers at higher concentrations of O2 that upon photolysis produce ozone.