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Measurement of Concentration of Singlet Molecular Oxygen in the Gas Phase by Electron Paramagnetic Resonance

Mikio Yagi, Syougo Takemoto, Ryouji Sasase
2004 Chemistry Letters  
The concentration of the lowest excited state of molecular oxygen, O 2 ( 1 Á g ), generated by gas-phase photosensitization with octafluoronaphthalene has been determined by electron paramagnetic resonance spectroscopy. The ground-state oxygen molecule, O 2 ( 3 AE g À ), was used as a quantitative standard. At low pressures, %0:12 Torr, about 30% of O 2 ( 3 AE g À ) was converted to O 2 ( 1 Á g ) under steady-state conditions. The lowest electronically excited singlet state of oxygen molecule,
more » ... f oxygen molecule, O 2 ( 1 Á g ), has been a subject of study for many years, with particular interest being taken in many photochemical and biological problems. 1-5 O 2 ( 1 Á g ) is an active intermediate in the photooxygenation reactions. It is important to measure the concentration of O 2 ( 1 Á g ) for most applications requiring O 2 ( 1 Á g ) as a reactive intermediate. 6 There are several methods for detecting O 2 ( 1 Á g ) in the gas phase and in condensed phases. The IR emission (a 1 Á g ! X 3 AE g À transition) spectroscopy is the most widely used technique to detect O 2 ( 1 Á g ). 7 However, since the ground-state oxygen molecule, O 2 ( 3 AE g À ), is recommended as a quantitative standard, the most reliable technique for determining O 2 ( 1 Á g ) concentration has been electron paramagnetic resonance (EPR) spectroscopy. [8] [9] [10] [11] In the present study, we have observed the EPR spectra of O 2 ( 1 Á g ) in the gas phase. Oxygen in the 1 Á g state can be detected using the EPR technique, because O 2 ( 1 Á g ) is paramagnetic owing to its orbital angular momentum. The first-order energy for the interaction of the magnetic moment associated with the total angular momentum J and an external magnetic field B can be described by the following equation: 8,12,13 E ¼ ðà þ 2AEÞðà þ AEÞ JðJ þ 1Þ
doi:10.1246/cl.2004.152 fatcat:fm3flqpwmjcinlsky3kmx4e6di