Nobuaki Kanamaru

Nuclear coordinate dependence of electronic transition moments involving torsional modes: the Franck–Condon/symmetry forbidden m03+ band in the allowed S1←S0 transition of toluene

Abstract A novel theory of vibronic intensity borrowing by large-amplitude vibrations was developed in a form to modify the conventional Herzberg–Teller theory. The ingredients are: (1) Crude Born–Oppenheimer wavefuntions (CBO Wf’s) at more-than-one (2×2×3=12) conformations were used as building blocks of the adiabatic BO Wf. (2) The latter was made to belong to the molecular symmetry group ( G 12 ) by Fourier-series expansion terminated at the low (ninth) order. (3) The non-Born–Oppenheimer effect was shown to be less significant. The experimental observation of the subtitle was successfully interpreted with this formalism, endorsing the previous assertion by Walker et al. [J. Chem. Phys. 102 (1995) 8718].

Rotational effect on radiationless transition. II. Typical intermediate case, pyrazine☆

Abstract A general theory of radiationless transitions to describe the rotational effect (including intramolecular vibrational redistribution and intramolecular vibration-rotation energy transfer) is presented, by using a Green-function technique on a multiple number of doorway states. According to the formalism based on molecular-eigenstate spectra, the typical intermediate-case decay behavior of pyrazine after picosecond excitation into lower rotational levels belonging to its S 10 level is examined. The so-called axis-switching, i.e. the intensity mixing mechanism between rotational levels due to electronic-state dependences of Eckart equations is appreciated as a prerequisite for multiple doorway states and is successfully applied for a model calculation of the above subject.

Rotational effect on radiationless transition. III. external magnetic-field effect

Abstract The theory of the rotational effect on radiationless transitions in typical azines is extended to include the external magnetic-field effect. By choosing the best experimental framework with a polarizer set parallel to the magnetic field and assuming an isotropic Zeeman Hamiltonian, the Zeeman effect on the formalism is found to be not so significant. The only change in the introduction of new kinds of matrix elements among triplet { t } levels that modify the distribution of molecular eigenstates (MESs) coupled to the doorway states { s }. The effect is rather perceived when we evaluate the m J dependence. Namely, the external magnetic-field effect in the decay behavior is recognized to be an incoherent superposition of 2 J + 1 individual processes with the m J dependencies. Experiments on the best framework by taking account of polarization are urged.

Time-resolved fluorescence spectra of a bichromophoric molecule, 2-methyl-1,2,3,4-tetrahydroisoquinoline in various media

Abstract Time-resolved fluorescence spectra of a title molecule (with benzene and aliphatic amine parts) in various media, after excitation by several lasers were observed to complement the previous work by conventional spectroscopy [N. Kanamaru, J. Tanaka, J. Phys. Chem. 95 (1991) 6441]. Though complex with many new features, the results were roughly consistent with the previous ones. The significant conclusions are as follows: (1) The emission to be ascribed to the amine (N) part, with more than one component (of nN and aN types) is observed not only for the acetonitrile solution (as previously reported) but also for all the other media. (2) Contrary to the case of a nonpolar hexane solution, both of N fluorescences in the other media reveal unusually long-lived decay components. This can be interpreted by assuming the so-called charge-transfer-to-solvent (CTTS) state that is nonfluorescent and lies just below the fluorescent state. (3) This observation in the protic media can also be taken as another evidence of the peculiar hydrogen bonding between this amine and the protic solvent molecules [N. Kanamaru, J. Tanaka, J. Phys. Chem. 95 (1991) 6441]. (4) Thus, the unexpectedly large quantum yields of N fluorescences in the polar media are now interpreted as arising due to the slow S 1 N →(CTTS)→S 0 internal conversions.

Long-lived fluorescence decay components in glyoxal

Abstract Long-lived components in glyoxal are considered to have been observed in the recent sensitized phosphorescence experiments reported by Ito and co-workers; this interpretation explains the apparent collision-free “intersystem crossing”, which is inconsistent with the accepted idea that glyoxal behaves according to the weakly coupled small-molecule limit. Mode selectivity as well as rovibronic level selectivity is also interpreted.