The effects of collision energy, vibrational mode, and vibrational angular momentum on energy transfer and dissociation in NO2+–rare gas collisions: An experimental and trajectory study

Abstract

A combined experimental and trajectory study of vibrationally state-selected NO 2 + collisions with Ne, Ar, Kr, and Xe is presented. Ne, Ar, and Kr are similar in that only dissociation to the excited singlet oxygen channel is observed; however, the appearance energies vary by ϳ4 eV between the three rare gases, and the variation is nonmonotonic in rare gas mass. Xe behaves quite differently, allowing efficient access to the ground triplet state dissociation channel. For all four rare gases there are strong effects of NO 2 + vibrational excitation that extend over the entire collision energy range, implying that vibration influences the efficiency of collision to internal energy conversion. Bending excitation is more efficient than stretching; however, bending angular momentum partially counters the enhancement. Direct dynamics trajectories for NO 2 + + Kr reproduce both the collision energy and vibrational state effects observed experimentally and reveal that intracomplex charge transfer is critical for the efficient energy transfer needed to drive dissociation. The strong vibrational effects can be rationalized in terms of bending, and to a lesser extent, stretching distortion enhancing transition to the Kr +-NO 2 charge state.

Vibrational effects on the reaction of NO2+ with C2H2: Effects of bending and bending angular momentum

“…CID has a threshold of 2.85 eV for the spinforbidden channel producing O͑ 3 P͒, whereas the spinallowed channel is inaccessible in our study ͓E 0 for O͑ 1 D͒ production= 4.82 eV͔. We recently studied CID of NO 2 + in collisions with rare gases, 2 and found that the spin-forbidden channel is reasonably efficient for Xe, presumably due to the strong spin-orbit coupling in this fourth row atom; however, for Kr and the lighter rare gases, only the spin-allowed channel is observed. In fact, for Ne and Ar, the CID cross section is insignificant for E col below ϳ8 eV, thus it seems unlikely that CID contributes significantly to the NO + signal or branching ratio for the energy range here.…”

“…When measured over a range of collision energies ͑E col ͒, and combined with theory, the mechanism can be unraveled in detail. 2,3 While there is now a significant body of work probing effects of vibrational excitation mode on different classes of reactions, there is little information about the effects of vibrational angular momentum associated with bending of linear molecules. A number of studies of effects on energy transfer in low energy collisions have been reported, 4 however, we are aware of only two previous studies looking at effects on reactions.…”

The mechanisms of collisional activation of ions in mass spectrometry

“…Exciting one particular vibration may make the ion more ''product-like'' and this can influence the course of the reaction. This was especially evident in the collision between NO þ 2 and the noble gases (Liu et al, 2006a). Excitation of the bending mode in NO þ 2 led to distortion of the resulting collision complex with Kr that favored charge transfer to form a Kr þ /NO 2 complex.…”

“…Velocity maps can be created which give information on the degree of forward and backward scattering of the product ions. Several systems have been studied including CH 2 CO þ /Ne, Xe (Liu, Devener, & Anderson, 2002); CH 3 CHO þ / C 2 D 4 (Kim, Liu, & Anderson, 2002); CH 2 CO þ /C 2 D 4 (Liu, Devener, & Anderson, 2004); CH 2 CO þ /CH 4 ; C 2 H þ 2 =CH 4 ; CH 2 CO þ /C 2 H 2 (Liu, Devener, & Anderson, 2005); NO þ 2 =Ne, Ar, Kr, Xe (Liu et al, 2006a); CH 2 CO þ /CO 2 (Liu et al, 2006b). They have developed a theoretical model for the velocity maps that appears to capture the basics of the physics of the interaction between the ion and neutral in these systems.…”

Theoretical Methods for Vibrational Spectroscopy and Collision Induced Dissociation in the Gas Phase

“…It is also interesting to note how the energy transfer is affected by collision orientation and, to some extent, the initial vibrational preparation of the ion. Full QM studies can be applied to relatively small systems, with the advantage of being able to describe in detail the effects of projectile nature in reactivity without any parameterization and taking into account the possibility of charge transfer to the ion, as pointed out by Anderson and co-workers studying the reactivity of NO þ 2 with rare gases [182].…”