Oxygen radiative lifetime

Fig. 34 Photosensitized singlet oxygen production 1/ r is the general (radiative and non-radiative) rate constant of the transition Si So fcsi is the rate constant of singlet-triplet conversion tt is the lifetime of the triplet, T1, electronic state of PS kj is the second-order rate constant of singlet oxygen quenching of the Ti state of PS tl and nr are the radiative lifetime and rate constant of all intramolecular nonradiative energy relaxation processes of O2 ( Ag)...

Arnold et al.24 have calculated radiative lifetimes for the various collision complexes of singlet molecular oxygen on the basis of a collision time of 10"13 sec. The data for wavelengths and transition probabilities are presented in Table III. A recent paper25 describes the theory of double electronic transitions, and gives calculated oscillator strengths for the oxygen systems. 

Because of the long radiative lifetime of the lowest triplet state, most phosphorescence in fluid solutions is obviated by collisional quenching, especially by dissolved molecular oxygen. Phosphorescence, when it occurs, is usually observed at low temperatures (e.g., that of liquid nitrogen) in rigid matrices where it may demonstrate high quantum yields. In the past three decades, much interest has been focused on phosphorescence at room temperature (RTP), which sometimes can be observed in samples adsorbed on solid substrates such as filter paper. Unfortunately, the quantum yields observed in room temperature phosphorescence are low, leading to poor analytical sensitivity, and the method has not enjoyed wide popularity. Phosphorescent measurements at low temperatures... 

The 0( D) atom is a mctastablc sj)ccics vit,h a radiative lifetime of about 150 s. This species, with the ground 0( P) state of atomic oxygen, is an important constituent of several dilute media, such as the interstellar medium and the upper atmosphere. The rate constants of 0( D) 4 Ho, CH4, H2O and N2O reactions is much larger than for O( P) with the same species. Thus, even if 0( D) atoms are less abundant than 0( P), they play an important role in astrochemistry. They give highly reactive radical j)roducts as OH or NO which are for instance responsible for a significant reduction of the Eartlds ozone layer. The 0( D)+H2 reaction is also important in combustion chemistry. 

The chemical loss of 02(1Ag) produces a ground state oxygen molecule. Since 02 is a permanent gas always present at a constant mixing ratio in the middle atmosphere, this process is not photochemically important. Further, the lifetime of 02(xAg) is never more than its radiative lifetime of about an hour, so that photochemical steady state (see Eqs. (2.37) and (5.27)) may be assumed for this species ... 

Table 2-5. Data Regarding Excited Oxygen Atoms (a) Known Production Processes (b) 298 K Quenching Coefficients, Radiative Lifetimes rR, and Altitudes for Equivalent Loss Rates for Quenching by Collisions versus Radiative Emission (c) Emission Altitudes... 

The reaction between barium vapour and oxygen has been used as a source of electronically excited BaO by Johnson [272], who measured the radiative lifetime and electronic quenching cross-sections of the BaO (A S) state. Obenauf et al. [273] have shown that the production of BaO (A S) from reaction of barium and oxygen is a complex process. 

Once produced, this singlet state of oxygen can be transported for considerable distances even at moderately high pressures, as the radiative lifetime is 64 min and 02(a A) is very resistant to collisional deactivation. Thus, 02(a A) is ametastable energy reservoir. Energy densities of 10-20 kJ/m are typically attained. 

Although direct photoinduced transitions in free molecular oxygen from the triplet to the singlet states are forbidden by selection rules, these transitions occur due to perturbations. Absorption and emission bands related to and A transitions, which occur at 7,882 cm and 13,121 cm have been observed in the upper atmosphere spectmm (Kearns 1971). The radiative lifetimes of A and states are 2.7 x 10 s and 7.1s (Kearns 1971 Huie and Neta 2002). The state quenches very rapidly... 

Badger RM, Wright AC, Whitlock RF (1965) Absolute intensities of the discrete and continuous absorption bands of oxygen gas at 1.26 and 1.065 p and the radiative lifetime of the Ag state of oxygen. J Chem Phys 43 4345-4350... 

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