Velocity map imaging of ion-molecule reaction products: Co+(3F4)+isobutane

Abstract

The velocity map imaging technique is applied to mass-selected CoC3H6++CH4 and CoC4H8++H2 elimination products from the Co+(3F4)+isobutane reaction studied under crossed-beam conditions at 0.21 eV collision energy. For both reactions we obtain the joint scattering probability distribution P(E,Θ), where E and Θ are the product translational energy and scattering angle. The fraction of available energy deposited into product translation is 0.4 for H2, compared with 0.1 for CH4. For the CH4 product, the angular distribution is forward-backwards symmetric and sharply peaked at Θ=0 and 180°. P(E,Θ) is not separable into the product of an energy and an angular function; rather, the angular distribution peaks more sharply at higher translational energy. Evidently, incipient CoC3H6++CH4 products equilibrate in the Co+(C3H6)(CH4) exit-channel well, from which they decay statistically. The product translational energy distribution P(E) is consistent with orbiting-transition state phase-space theory with no exit-channel barrier. In addition, the energy-integrated angular distribution T(Θ) is consistent with the predictions of the early statistical complex decay model of Miller and Herschbach for fragmentation from a transition state that is a prolate top. In sharp contrast, P(E) for the CoC4H8++H2 products exhibits a substantial hot, nonstatistical tail towards high energy. Perhaps the H2 channel has a late potential energy barrier some 0.5 eV above products, but we view this explanation as highly unlikely. Instead, we suggest that the potential energy from an earlier multicenter transition state is funneled efficiently, and highly nonstatistically, into product translation. This surprising conclusion may apply to H2 products for the entire family of reactions of the late-3D series transition metal cations Fe+, Co+, and Ni+ with alkanes.

Imaging ion-molecule reactions: Charge transfer and halide transfer reactions of O+ with CH3Cl, CH3Br, and CH3I

“…Detecting products at variable delay times after extracting products from the collision region allows products of different masses to be imaged. The experimental method is similar to schemes employed in other laboratories [21][22][23][24][25][26].…”

Ion imaging study of dissociative charge transfer in the N2+ + CH4 system

“…The experimental method is based upon important developments from other laboratories. [15][16][17][18][19][20] The primary ion beam is formed by impact of 90 eV electrons on a mixture of 10% N 2 in He. 21 The primary product of electron impact on this mixture is He + , which then undergoes charge transfer with N 2 to form both parent (N 2 + ) and fragment (N + ) ions.…”

Imaging the dynamics of ion–molecule reactions

“…The reactivity of hydrocarbons in reactions with transition metal ions has already been investigated for several decades. [98][99][100] The group of James Weisshaar extended their experiments with crossed beams [101][102][103][104][105] to investigate the reaction of the cobalt cation with small saturated hydrocarbon molecules using velocity map imaging: 30,106 Co…”

“…In their experiment the cations were created by pulsed laser ionization directly in the interaction region. 30 In the experiment that we have set up a few years later a spatially separated ion source was employed, 31 which had also been the concept used in previous experiments employing rotatable detectors. This yields a lot of flexibility to create and control different ionic species, in particular also negative ions.…”