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单重态O_2（^1Δ_g）是一个长期的研究课题，在许多光化学和生物学问题中引起了人们的兴趣。O_2（^1Δ_g）是光氧化反应的活性中间体。对于大多数需要O_2（^1 Δ_g）作为反应中间体的应用来说，测量O_2（^1 Δ_g）的浓度是很重要的。由于基态氧分子O_2（^3 Δ_g^-）被推荐为定量标准，因此测定O_2（^1Δ_g）浓度的最可靠的技术是电子顺磁共振（EPR）谱。由于O_2（^1 Δ_g）的轨道角动量是顺磁性的，所以用EPR技术可以检测到处于^1Δ_g态的氧。O_2（^1 Δ_g）分子是由O_2（^3 Δ_g^-）通过激发三重态的敏化剂分子的气相能量转移生成的。萘、1-氟萘、八氟萘和二苯甲酮被用作 ...更多信息 用作敏化剂。在JEOL JES-FA 200 X波段谱仪上，采用Varian V-4535大型进样圆柱腔和自制的100 kHz功率放大器，在室温下测量了样品的EPR谱。用Canrad-Hanovia 1 kW Xe-Hg弧光灯激发，在1 T左右激发时观察到O_2（^1Δ_g）的特征四线EPR谱。O_2（^3 Δ_g^-）的EPR信号在激发时随O_2（^1Δ_g）信号的升高而迅速下降。关闭激发光后，O_2（^3 Δ_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（^3 Δ_g^-）可以忽略不计。我们可以有把握地假定，在除^1Δ_g以外的某些亚稳态中，O_2的量是可以忽略的。因此，我们直接估算了O_2浓度（^1Δ_g）。在我们的实验条件下，用八氟萘在低压（约等于0.3Torr）下光敏化，获得了40%的稳态O_2（^1Δ_g）浓度。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