Photodissociation of singlet oxygen in the UV region

Abstract

Photodissociation of singlet oxygen, O2 a(1)Δg, by ultraviolet radiation in the region from 200 to 240 nm has been investigated using velocity map imaging of the atomic oxygen photofragments. Singlet oxygen molecules are generated in a pulsed discharge and studied by one-laser photodissociation and detection around 226 nm as well as two color photodissociation at various wavelengths in the range from 200 to 240 nm. A simple model of the discharge on and off signal indicates efficient conversion of O2 X(3)Σg(-)(v = 0) in the parent beam to O2 a(1)Δg(v = 0-2). Minute amounts of highly excited vibrational levels of ground state O2 X(3)Σg(-)(v > 0) are detected but no evidence is found for production of the O2 b(1)Σg(+) state. Over the decreasing wavelength range 240-200 nm the a(1)Δg-state signal relative to the X(3)Σg(-)(v = 0) signal decreases strongly. Around 226 nm the a(1)Δg(v = 0-2) states averaged branching ratio percentage for O((3)Pjj = 2 : 1 : 0) is found to be 56 : 36 : 8 (±5%), respectively. The anisotropy parameter for photodissociation of a(1)Δg(v = 0-2) averages to β = 1.3 ± 0.4. The a(1)Δg(v = 0) photodissociation cross section is found to 3-10 times stronger than theory predicts. Furthermore, the photodissociation image shows a strong parallel character, (i.e., transition moment parallel to the molecular axis) while theory predicts a predominantly negative character.

Spectral dependence of the efficiency of direct optical excitation of molecular oxygen in tetrachloromethane

“…Apparently, these phenomena at very high density of excitation laser radiation (used in this study) can be supplemented with photolysis of molecular oxygen in both the O 2 ( 3 Σ g ) ground state [32,[40][41][42] and the O 2 ( 1 Δ g ) excited singlet state [43], which may occur (as the singlet oxygen production) during two-photon absorption of optical excitation radiation by an oxygen molecule or its van der Waals complexes with solvent [44]. At the same time, taking into account the presence of the solvent, the contribution from molecular-oxygen photolysis to the total decrease in the luminescence intensity of singlet oxygen and the decrease in its lifetime in the excited state cannot be much larger than the influence of photolytic decomposition of the solvent because the absorption cross section of CCl 4 molecule in the spectral range coinciding with the Herzberg band is larger than that of oxygen molecule by two to three orders of magnitude [37].…”

First-principles calculation of correlated electron materials based on Gutzwiller wave function beyond Gutzwiller approximation

“…Fig. 3 plots the binding energy curve of GCGM+Ec and the large basis CI [60] for comparison, where close agreement is established again (the binding energy error is 0.0022 and 0.0027 Hartrees for singlet and triplet, respectively).…”

“…Potential energy curves of triplet and singlet oxygen with GCGM+Ec and large basis CI[60] for comparison.…”

Singlet oxygen photogeneration from X–O2 van der Waals complexes: double spin-flip vs. charge-transfer mechanism

“…That is why mechanisms (8)- (10) do not work in a molecular beam. Molecules of oxygen excited into the Herzberg state via process (8) in the solvent can then collide with the dissolved ground state O 2 molecules giving rise to singlet oxygen in a process (10) discussed by Trushina et al 40 for the gas phase. This should universally take place in the gas or condensed phase in the spectral region of Herzberg absorption at wavelengths below 290 nm.…”