Photofragment spectroscopy of molecular ions: design and performance of a new apparatus using coaxial beams

Direct photodissociation of SO+ via the 14Σ+ state

“…The SO ÷ ions are produced by dissociative ionisation of SO 2 by electron impact. Our work on H~- [14] has shown that in our low-pressure discharge source the vibrational population is compatible with single electron-impact conditions, i.e. significant vibrational relaxation does not take place.…”

“…Secondly, the mass ratio of the observed fragment ion and the neutral fragment in the present case (ms+ =2too) is unfavourable for the attainable energy resolution. These effects have been explicitly discussed in [14]. Further improvement of the measurements is presently limited by the lifetime of the cathode and the available intensity.…”

“…1 and 2 have been obtained at a primary beam energy of To = 600 eV following our discussion of the optimum choice of apparatus parameters in [14]. We also performed these measurements at higher primary beam energies, but the spectra did not show any evidence for vibrationally resolved structure.…”

“…The laser-ion photofragment spectrometer used in the present measurements has been described in detail previously [14]. The SO + ions are formed in a lowpressure hot-filament discharge source, mass selected by a Wien filter, and then energy selected by a double electrostatic monochromator of the 180 ° hemispherical type [15-1.…”

“…Using our recently developed ion photofragment spectrometer [14], we have measured the kinetic energy distribution of S + fragments arising from the direct photodissociation process SO + (a 4//) + h v ~ S + + O via the 142 + state. The vibrational levels v=7-13 of the initial a 411 state are observed in the spectrum and the results support the molecular constants deduced by Cosby [13].…”