T. Glenewinkelmeyer et al., MASS-DEPENDENT DYNAMICS OF THE LUMINESCENT EXCHANGE-REACTIONS C-2), P+(P-3)+H-2, D-2, HD((P), International journal of mass spectrometry and ion processes, 144(3), 1995, pp. 167-197
Citations number
45
Categorie Soggetti
Spectroscopy,"Physics, Atomic, Molecular & Chemical
Chemiluminescent ion/molecule reactions of ground state C+ and P+ ions
with H-2, D-2 and HD have been studied in an ion beam/target gas cell
arrangement. Emission spectra of CH+, CD+ (A (II)-I-1) and of PH+, PD
+ (A (2) Delta) were observed with up to 1 Angstrom FWHM resolution an
d at collision energies from threshold (approximate to 3 eV) to 8 eV(c
.m.) (centre-of-mass) and 15eV(c.m.), respectively. Very detailed comp
uter simulations of the spectral contours were done, including ab init
io transition moments and, in the case of PH+/PD+, the effects of pred
issociation. In simulating the spectra obtained with HD, the overlappe
d hydride and deuteride product ion spectra could be isolated by varyi
ng the respective weighting factors to achieve an optimum overall fit.
In the case of C+ + HD, the two components were found to have very si
milar rovibrational distributions as with the products from C+ + H-2 a
nd C+ + D-2 In the P+ case, however, the rotational, although not the
vibrational, distributions were found to be significantly different fo
r the isotopically mixed and the pure reactions. The cross-sections sh
owed an intermolecular isotope effect only for C+ + H-2 VS. C+ + D-2 a
t high energies. However, both with C+ + HD and P+ + HD, a very strong
intramolecular isotope effect, i.e. an energy-dependent branching rat
io, was observed: at low energies deuteride formation prevails, at hig
h energies hydride. This behaviour is discussed in terms of an impulsi
ve collision model, assuming the ''pairwise'' relative kinetic energy
between the reacting atoms to be the determining factor. On the basis
of the measured cross-section curves for the H-2 and D-2 reactions, th
e energy-dependent hydride/deuteride ratio in the HD reaction can then
be predicted. The agreement with the experimental results is excellen
t in the P+ case, but only moderate for the C+ reactions. Even the Preaction, however, does not occur via the spectator stripping mechanis
ms. The spectra show an energy-independent vibrational excitation, con
trary to the stripping model assumption. The impulsive model was also
extended to an analysis of the relative mean product angular momenta.
Again it performs well for P+ + H-2, D-2, HD, but cannot fit the C+ HD case.