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The conformational property of ethoxybenzene has been investigated by means of the laser-jet spectroscopy and the theoretical calculations. The quantum-mechanical analysis of the two-dimensional potential surfaces for the S 0 and S 1 states that have been obtained from the DFT and TDDFT calculations, respectively, has been carried out. Its result suggested the existence of the second conformer ( gauche ) in addition to the main conformer ( trans ) in the both states, and it was predicted that the 0–0 band of the gauche conformer would appear at about 400 cm −1 lower than that of the trans conformer. The S 1 ← S 0 fluorescence excitation spectrum of jet-cooled ethoxybenzene has been measured. The peak that is assignable to the 0–0 band of the second conformer has been observed, whose spectral position (red-shifted from that of the trans conformer by about 229 cm −1 ) is qualitatively consistent with the theoretical prediction.

The ground and low-lying excited states of Na(NH3)n and Na(H2O)n (n = 1–8) clusters were studied using ab initio molecular orbital methods. The calculated vertical transition energies to the 32P(Na)-type states agree well with the energies of the absorption maxima. The clusters change from a valence state to a two-center state via a diffuse one-center state with increasing n in both the ground and excited states. The localization of an unpaired electron proceeds at a faster rate against n in Na(H2O)n than in Na(NH3)n. The formation of an excited state of the solvated electron is found in Na(H2O)4–8.

New optical emission spectra of linear carbon molecules, polyynes C2nH2 (n = 5–8), were observed upon UV-laser excitation of the 0–0 band of the dipole-allowed transition, 1 Σ u + ← X 1 Σ g + , of size-separated polyyne molecules in hexane. The emission spectra of C10H2 showed distinct peaks at 436 and 480 nm with a separation of ∼2100 cm−1 for a stretching vibration of the sp-carbon chain. Weak absorption features were also recorded in near-UV regions in shorter wavelengths to compare with the emission spectra. The spectral features in the emission were assigned to the vibronic bands of the forbidden electronic transition, 1 Δ u → X 1 Σ g + .

Intermolecular magnetic interactions through hydrogen bonding of the carboxy group for dimers of allyl, benzyl, and chlorinated benzyl radicals have been investigated as model systems by the ab initio molecular orbital (MO) and density functional theory (DFT) calculations. It is found possible to propagate magnetic interaction through hydrogen bonding, although the effect is small. The spin densities of π- and σ-electrons have shown that antiferromagnetic coupling exists between the two intermolecular oxygen atoms in the ground state. This behavior is consistent with McConnell’s model, being applied to the planar configuration of the two hydrogen-bonded carboxy groups.

Picosecond time-resolved IR spectra of phenol–(NH3)3 have been measured by UV–IR–UV ion dip spectroscopy for the first time. It was found that the time-evolution of two vibrational bands at 3180 and 3250 cm −1 is different from each other. The results show that two transient species are generated from the photo-excited phenol–(NH3)3 cluster. From ab initio calculation, the transient species are assigned to two isomers of (NH3)2NH4.

We have investigated geometries, ionization potentials (IPs), and vertical transition energies (VTEs) of NH 4 ( NH 3 ) n (n=0–4) cluster radicals by ab initio MO method at the correlated level. The structures in which NH4 donates as many NH bonds as possible to the hydrogen bonding with surrounding NH3 molecules are the most stable for each n. The calculated IPs agree well with experiment. The spatial expansion of the unpaired electron occurs with stepwise solvation. The growing one-center Rydberg-like nature of the cluster radicals results in the successive decrease in the transition energies to the low-lying excited states, which is responsible for the red shifts of the electronic absorption bands.