Matrix-isolated oxygen: Line-shapes and transition probabilities of the b1∑g+→X3∑g−, b1∑g+→a1Δg and a1Δg→X3∑g− transitions

Singlet oxygen generation by nanoporous silicon: photoluminescence dynamics in magnetic field

Singlet oxygen generation in porous silicon (PSi) was investigated by a magneto-optical experiment. Photoluminescence (PL) quenching due to an energy transfer (ET) process mediated by an exchange interaction was monitored in the spectral range 1.4-2.5 eV and in a magnetic field of 0-6 Tesla at different levels of oxygen concentration and excitation pump power. When a magnetic field was applied, both PL recovery and, for magnetic fields below 2 Tesla and high concentrations of oxygen, an unusual additional pump power dependent quenching of the PL was observed. A rate equation model describing the behavior of PL from PSi with oxygen adsorbed at cryogenic temperatures in magnetic field was developed. The model has been expanded to cover the ET process as a function of the nanoparticle size.

Response calculations of electronic and vibrational transitions in molecular oxygen induced by interaction with noble gases

The Einstein coefficient for the singlet oxygen emission a1Deltag-->X3Sigmag- at lambda=1270 nm and b1Sigmag+-->X3Sigmag- emission at lambda=750 nm were calculated by quadratic response (QR) multiconfiguration self-consisted field (MCSCF) method for a number of collision complexes O2+M, where M=He, Ne, Ar. Interaction with He clusters was studied in order to simulate cooperative effect of the environment on the oxygen emission. Calculations of the dipole transition moment for the Noxon band, b1Sigmag+-a1Deltag, by linear response (LR) MCSCF method were also performed for a number of collision complexes. Spin-orbit coupling (SOC) between the b1Sigmag+ and X3Sigmag- (MS=0) states does not change much upon collisions, thus the a-X transition borrows intensity mostly from the collision-induced Noxon band b-a. The a-X intensity borrowing from the Schumann-Runge transition is negligible. The calculations show that the b-a and a-X transition probabilities are enhanced approximately by 10(5) and 10(3) times by O2+M collisions. An order of magnitude differences occur for both transitions for noble gases with large difference in polarizability. A strong cooperative effect is obtained when few He atoms perturb the oxygen molecule. Depending on mutual orientation of the partners it can be a complete quenching of the a-->X emission or strong non-additive enhancement. Collision-induced infrared vibrational transitions in a number of molecular oxygen excited states were studied and shown to be state selective.

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.