Articles you may be interested in K selection in one-photon mass-analyzed threshold ionization of C H 3 I and C D 3 I to the X ̃ E 3 ∕ 2 2 state cations J. Chem. Phys. 128, 044310 (2008); 10.1063/1.2823032 Diradicals, antiaromaticity, and the pseudo-Jahn-Teller effect: Electronic and rovibronic structures of the cyclopentadienyl cationThe Jahn-Teller effect in the lower electronic states of benzene cation. II. Vibrational analysis and coupling constants of the B̃ 2 E 2g state Photoinduced Rydberg ionization ͑PIRI͒ spectroscopy has been applied to the problem of recording vibrationally resolved spectra of the dipole-forbidden B 2 E 2g ←X 2 E 1g transition of C 6 H 6 ϩ and C 6 D 6 ϩ . PIRI spectra of the B state have been recorded via a number of vibrational states of the ionic ground state. A combination of Herzberg-Teller and pseudo-Jahn-Teller vibronic coupling between the B state and a close lying C state were used to explain the complex B state vibrational structure. The two pseudo-Jahn-Teller vibrational modes, 16 and 17 , were both found to be active in the PIRI spectra. In addition, evidence for a strong pseudo-Jahn-Teller interaction within each of these modes was found. The perturbed vibronic bands resulting from this pseudo-Jahn-Teller activity were successfully modeled using a two-mode pseudo-Jahn-Teller vibronic coupling model. Using a combination of the spectral results and the pseudo-Jahn-Teller calculations, we were able to generate absolute vibronic symmetry assignments for many of the lower B state vibrational levels, from which vibrational assignments were made. The calculations also produced unperturbed vibrational frequencies for both pseudo-Jahn-Teller active modes along with values for their respective linear coupling constants.

Pump-probe delayed ionization studies on phenylacetylene and benzonitrile in a supersonic beam reveal the production of a low-ionization-potential (approximately 5.7 eV) species lasting more than hundreds of microseconds after excitation to the S1 state. Excitation of the molecules was done with a frequency-doubled, Fourier transform-limited, pulse-amplified cw laser, and the rotationally resolved structure of the S1-S0 transition ensures that the excited molecules are monomers. Excited-state photoelectron spectroscopy shows that the long-lived species are formed during the light pulse but not by transfer from the fluorescing S1 population after the pulse, even though the S1 spectral signature is present in the long-lived action spectrum. This behavior differs greatly from that found in benzene and with most commonly held pictures of radiationless transitions in large molecules.