Direct Detection of Singlet Molecular Oxygen by Electron Paramagnetic Resonance and Development of a New Quantitative Method for the Concentration Measurement

氧分子的最低电子激发态O_2（^1Δ_g）是一个研究多年的课题，在许多光化学和生物学问题上引起了特别的兴趣。O_2（^1Δ_g）是光氧化反应中的活性中间体。对于大多数需要O_2（^1Δ_g）作为反应中间体的应用来说，测量O_2（^1Δ_g）的浓度是很重要的。由于基态氧分子O_2（^3Σ_g^-）被推荐作为定量标准，所以测定O_2（^1Δ_g）浓度最可靠的技术是电子顺磁共振（EPR）光谱。^1Δ_g态的氧可以用EPR技术检测到，因为O_2（^1Δ_g）由于其轨道角动量是顺磁性的。O_2（^3Σ_g^-）由敏化剂分子激发态的气相能量转移生成O_2（^1Δ_g）分子。以萘、1-氟萘、八氟萘和二苯甲酮为增敏剂。EPR光谱在室温下由JEOL JES-FA200 x波段光谱仪和瓦里安V-4535大样品进入圆柱腔进行测量。采用加拿大-哈诺维亚1 kW Xe-Hg电弧灯进行激励。O_2（^1Δ_g）在约1t激发时呈现出近对称的四线EPR谱特征。O_2（^3Σ_g^-）的EPR信号随着O_2（^1Δ_g）信号的升高而下降。在关闭激发光后，O_2（^3Σ_g^-）信号上升，O_2（^1Δ_g）信号消失。这些结果表明，与产生的O_2量（^1Δ_g）相比，激发时O_2的损失（^3Σ_g^-）可以忽略不计。我们可以有把握地假设，除^1Δ_g外，处于亚稳态的O_2的量可以忽略不计。因此我们直接估算了O_2的浓度（^1Δ_g）。在我们的实验条件下，用八氟萘在低压下（约等于）0.3 Torr光敏，得到稳态O_2（^1Δ_g）浓度为40%。少

The lowest electronically excited singlet state of oxygen molecule, O_2(^1Δ_g), has been a subject of study for many years, with particular interest being taken in many photochemical and biological problems. O_2(^1Δ_g) is an active intermediate in the photooxygenation reactions. It is important to measure the concentration of O_2(^1Δ_g) for most applications requiring O_2(^1Δ_g) as a reactive intermediate. Since the ground-state oxygen molecule, O_2(^3Σ_g^-), is recommended as a quantitative standard, the most reliable technique for determining O_2(^1Δ_g) concentration has been electron paramagnetic resonance(EPR) spectroscopy. Oxygen in the ^1Δ_g state can be detected using the EPR technique, because O_2(^1Δ_g) is paramagnetic owing to its orbital angular momentum.O_2(^1Δ_g) molecules were generated from O_2(^3Σ_g^-) by gas-phase energy transfer from the excited triplet states of the sensitizer molecules. Naphthalene, 1-fluoronaphthalene, octafluoronaphthalene, and benzophenone were u … More sed as the sensitizer. The EPR spectra were measured at room temperature by a JEOL JES-FA200 X-band spectrometer equipped with a homemade 100 kHz power amplifier and a Varian V-4535 large sample access cylindrical cavity. The excitations were carried out using a Canrad-Hanovia 1 kW Xe-Hg arc lamp.The characteristic nearly symmetrical four-line EPR spectrum of O_2(^1Δ_g) was observed at about 1 T during excitation. The EPR signals of O_2(^3Σ_g^-) decreased immediately with rise of O_2(^1Δ_g) signals on excitation. After shutting off the exciting light, the O_2(^3Σ_g^-) signals rose and the O_2(^1Δ_g) signals disappeared. These results show that the loss of O_2(^3Σ_g^-) on excitation is negligible compared to the amount of produced O_2(^1Δ_g). We can safely assume that the amount of O_2 in some metastable state other than ^1Δ_g is negligible. Therefore we estimated the concentration of O_2(^1Δ_g) directly. Under our experimental conditions, the steady-state O_2(^1Δ_g) concentration of 40% was obtained by the photosensitization with octafluoronaphthalene at low pressures, 【approximately equal】0.3 Torr. Less