Abstract
Previously reported “near-threshold” laser photofragment spectra of CH + near 540 nm are interpreted as arising from charge-transfer electronic transitions between levels lying just below the C + ( 2P)+H( 2 dissociation asymptote and a weakly bound long-range electronic state which correlates to the C ( 3P)+H + dissociation limit. The shallow well of the upper state is determined principally by the long-range attractive ion-induced-dipole and charge-quadrupole interactions between the carbon atom and the proton and shorter-range repulsive behaviour. In our interpretation, low-energy C + ions are detected following radiative decay of laser-excited CH + to continua just above the lowest dissociation limit. Experimental and theoretical evidence for this bound-bound-free process is presented. The characteristics of long-range weakly bound states and the role of non-adiabatic interactions near to dissociation are discussed. The possibility that previously observed laser photofragment spectra near 350 nm arise from a similar origin is considered.
Published Version
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