Intramolecular dynamics by photoelectron spectroscopy. I. Application to N+2, HBr+, and HCN+

The Fourier transform of an optical electronic spectrum leads to an autocorrelation function C(t) which describes the evolution in time of the wave packet created by the Franck–Condon transition, as it propagates on the potential energy surface of the electronic upper state. This correlation function is equal to the modulus of the overlap integral between the initial position of the wave packet and its instantaneous position at time. The original data resulting from an experimentally determined spectral profile must be corrected for finite energy resolution, rotational, and spin‐orbit effects. The behavior of the system can then be followed up to a time of the order of 10−13 s, i.e., during the first few vibrations which follow immediately the electronic transition. The method is applied to photoelectron spectra and the results are compared to the available information on potential energy surfaces of ionized molecules, in order to study their unimolecular dissociation dynamics. In the case of the X 2Σ+g, ...