Detection of the Fraunhofer band B (690 nm) in the absorption spectra of oxygen in aerated solvents

Benditkis, A.; Kozlov, A.; Goncharov, S.; Krasnovsky, J.; AA

Авторы: Benditkis AS, Kozlov AS, Goncharov SE, Krasnovsky Jr, AA
Журнал: Journal of the Optical Society of America B: Optical Physics
Том: 38
Номер: 11
Год издания: 2021
Издательство: Optical Society of America
Местоположение издательства: United States
Первая страница: 3410
Последняя страница: 3416
DOI: 10.1364/josab.432684
Аннотация: IR phosphorescence (1270 nm) and chemical trapping of singlet 11g .0/ molecular oxygen have been studiedin aerated organic solvents under laser irradiation at 690 nm and 765 nm, in order to reveal the Fraunhoferband B [16gC.1/ 36g􀀀.0/ transition] in the absorption spectra of dissolved oxygen molecules at normalconditions and compare its parameters with those of the previously observed Fraunhofer band A[16gC.0/ 36g􀀀.0/ transition]. Chemical trapping experiments were found to be inappropriate for solutionof this problem because complexes of the traps with oxygen were revealed, which were more photoactiveunder irradiation by red laser light than oxygen molecules themselves. Phosphorescence of singlet oxygenwas reliably detected under laser irradiation of aerated solvents at 690 nm. It was about one order weakerthan under excitation at 765 nm. However, in both cases, phosphorescence linearly depended on excitationpower, equally increased after oxygen purging and built up in the solvents containing heavy atoms (bromineand iodine). Similar phosphorescence decay times were observed under pulsed laser excitation at both 690and 770 nm. The data provide compelling evidence that phosphorescence arising under irradiation at 690nm is due to excitation of the Fraunhofer band B in the oxygen absorption spectrum. The molar absorptioncoefficient at the peak of this band was estimated to be 510􀀀5 M􀀀1 cm􀀀1 in the aerated solvents lackingheavy atoms. Thus, for the first time, absorption coefficients corresponding to the Fraunhofer band B ofdissolved oxygen were estimated in aerated solvents under natural conditions. This information is importantfor both spectroscopy of oxygen and mechanistic studies of biological and therapeutic action of laserradiation. ©2021 Optical Society of Americahttps://doi.org/10.1364/JOSAB.4326841. INTRODUCTIONIt iswell known that gaseous oxygen molecules in Earth’s atmospherehave very weak dark red and IR absorption bands peakingat 688, 762, 1067, and 1268 nm ([1–5] and references therein)(Fig. 1). The dark red bands at 688 and 762 nm (so-calledFraunhofer bands B and A) were first observed in 1802–1814by Wollaston and Fraunhofer as the strongest dark lines in thespectrum of solar radiation on the Earth’s surface.During morethan 80 years the origin, of these lines had been unknown. In1883–1885, Egoroff (St. Petersburg, Paris) experimentallyproved that these lines were due to absorption of solar radiationby atmospheric oxygen. In 1886–1888 this conclusionwas supported by Janssen (France) and then, by many otherresearchers ([1] and references therein). Based on these dataand principles of molecular orbital theory, Mulliken claimedthat the ground state of O2 molecules is triplet (36g􀀀), andthe absorption
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Detection of the Fraunhofer band B (690 nm) in the absorption spectra of oxygen in aerated solventsстатья