Infrared laser-induced photofragmentation of the positive and negative ions of size-selected SF6 (NO)n clusters

Abstract

A detailed study has been undertaken on the infrared photofragmentation of SF 6 (NO); cluster ions. A line-tuneable CO 2 laser has been used to excite the J)3 vibrational mode of the SF 6 molecule which is followed by the observation of three separate fragmentation channels: -SF(j, -NO, and -2NO. The relative intensities of the fragments are found to be sensitive to the sign of the charge on the ion, the cluster size, and whether n is either odd or even. Within clusters of the same charge, the most marked transitions in fragmentation pattern are found between odd-and even-sized cluster ions, with the decay channels favoring those processes which lead to the formation of even electron ions. There are also large differences in fragmentation pattern between the negatively and positively charged ions. A summation of fragment ion intensities as a function of laser wavelength is used to determine infrared absorption profiles and their shapes confirm a pronounced difference in behavior between SF 6 (NO); and SF 6 (NO);. The results for the positively charged ions are interpreted in terms of a central (NO): core which serves to fix the position of the SF 6 molecule via an attractive ion-induced dipole interaction. In contrast, observations on the negatively charged ions, suggest that the interaction between the excess electron and the SF 6 is predominantly repulsive and also sufficiently 'diffuse as to keep the molecule comparatively mobile even in large cluster ions. It is suggested that the excess electron in SF 6 (NO); may occupy a surface state and that the state has associated with it approximately 15 NO molecules.

The critical hydration reactions of NO+ and NO2+

“…6 MIKE ͑Mass-analyzed ion kinetic energy͒ spectra were recorded for each of the ions under conditions where both unimolecular and collisioninduced fragmentation patterns could be identified separately. For the clusters NO ϩ •͑H 2 O͒ 3-5 and NO 2 ϩ •͑H 2 O͒ 2-4 , the parent signals were reduced by approximately one-half through the introduction of collision gas ͑air at ϳ10 Ϫ6 mbar) into a cell located in the second field-free region between the magnet and the electrostatic analyzer.…”

Trapping and recording the collision- and photo-induced fragmentation patterns of multiply charged metal complexes in the gas phase

“…A disadvantage is that the technique is currently restricted to ligands that are volatile; however, some success has been obtained with a dual pick-up system where involatile ligands are held in a heated reservoir inside the vacuum chamber that houses the nozzle. 1 Previous experimental work has demonstrated that the use of argon as opposed, for example, to helium is crucial to the success of the pick-up technique [33], and separate molecular dynamics simulations have shown that cooling through argon atom evaporation is an integral part of the pick-up mechanism [34].…”

Infrared photofragmentation spectra of size-selected SF6⋅Ar+n cluster ions

“…In a series of recent papers [15][16][17][18] we have shown that, through the careful selection of cluster/chromophore combinations, it is possible to study the laser-induced infrared photofragmentation spectroscopy of single neutral molecules in association with mass-selected cluster ions. A necessary condition for the success of such experiments is that, for a chromophore Y and a cluster X n , the relative ionization energies ͑IE͒ are such that IE(Y )ϾIE(X n ).…”

“…A necessary condition for the success of such experiments is that, for a chromophore Y and a cluster X n , the relative ionization energies ͑IE͒ are such that IE(Y )ϾIE(X n ). [15][16][17][18] Under these circumstance, the cluster can be ionised in the knowledge that it is X n which carries the positive charge and, therefore, allows ions to be mass selected. However, through a suitable selection of chromophores, spectroscopic studies can be undertaken on a single molecule of Y that is cluster-bound and which, at the same time, has a gas-phase infrared spectrum that is well understood.…”

“…20,21 A further facet to these new experiments is the ability to make quantitative observations on laserinduced fragmentation patterns: persistent loss of the chromophore from a cluster as the size is incremented, 18 would suggest the molecule occupies a surface site and preferential decay to a particular cluster would imply the presence of a stable structure. 17 One disadvantage of the approach discussed here, is that the technique provides limited control over the internal energies of the cluster ions. The clusters, Y X n , are prepared as neutral species and then ionised by electron impact.…”