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Chemically induced dynamic electron polarization (CIDEP) generated through interaction of the excited triplet state of 1-chloronaphthalene, benzophenone, benzil, and Buckminsterfullerene (C60) with 2,2,6,6,-tetramethyl-1-piperidinyloxyl (TEMPO) radical was investigated by using time-resolved ESR spectroscopy. We carefully examined what factors affect the CIDEP intensities. By comparing CIDEP intensities of TEMPO in the 1-chloronaphthalene, benzophenone, and benzil systems with that obtained in the C60−TEMPO system, the absolute magnitude of net emissive polarization was determined to be −2.2, −6.9, and −8.0, respectively, in the units of Boltzmann polarization. In the 1-chloronaphthalene−TEMPO system, the viscosity effect on the magnitude of net polarization was studied by changing the temperature (226−275 K) in 2-propanol. The emissive polarization was concluded to result from the state mixing between quartet and doublet manifolds in a radical−triplet pair induced by the zero-field splitting interaction of the counter triplet molecule. The magnitude of net polarization is much larger than the polarization calculated with the reported theory that the CIDEP is predominantly generated in the region where the exchange interaction is smaller than the Zeeman energy. Our experimental results are quantitatively explained by the theory that the CIDEP is generated predominantly in the regions where the quartet and doublet levels cross. We propose a theoretical treatment to calculate the magnitude of net polarization generated by the level crossings in the radical−triplet pair mechanism under highly viscous conditions and perform a numerical analysis of the net RTPM polarization with the stochastic-Liouville equation. The viscosity dependence of the net polarization indicates that the back transition from the doublet to quartet states sufficiently occurs in the level-crossing region under highly viscous conditions. The estimated large exchange interaction suggests that the quenching of the excited triplet molecules by TEMPO proceeds via the electron exchange interaction.

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The bound–bound excitation spectrum of the NO–Ar van der Waals complex associated with the NO A 2Σ+–X 2Π transition has been measured by the resonance enhanced two-photon ionization (RE2PI) method using a time-of-flight (TOF) mass spectrometer. The van der Waals bands characterized by red-shaded rotational contours present no regularity in the progression. The photodissociation action spectra obtained by probing the NO A 2Σ+(v′=0, N′=1–8) products have also been measured, and the binding energies (D0) of the complex in the A 2Σ+ and X 2Π states are determined as 44 and 88 cm−1, respectively. The action spectrum corresponding to the NO A 2Σ+(v′=0, N′=1 and 2) product shows several shape resonance peaks, which implies that the intermolecular potential between NO A 2Σ+ and Ar has a potential barrier of about 24 cm−1.

Benzyl and its p-fluoro and p-methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p-fluorobenzyl shows quite similar vibrational structure to that of p-fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p-fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p-methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p-xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these radicals. Time profiles of the emission intensity of p-fluorobenzyl and p-methylbenzyl show single exponential decay and their lifetimes do not indicate significant dependence on vibronic levels. On the other hand, benzyl shows dual exponential decay, which is interpreted by intermediate coupling case behavior.