Partial Control of an Ion-Molecule Reaction by Selection of the Internal Motion of the Polyatomic Reagent Ion

Abstract

The ion-molecule reaction NH(3)(+) + ND(3) has been studied at various collision energies (1 to 5 electron volts in the center of mass) with preparation of the NH(3)(+) reagent in two nearly isoenergetic vibrational states. One state corresponds to pure out-of-plane bending of the planar NH(3)(+) ion (0.60 electron volts), whereas the other state is a combination of in-plane and out-of-plane motion (0.63 electron volts). The product branching ratios differ markedly for these two vibrational-state preparations. The differences in reactivity suggest that the in-plane totally symmetric stretching mode is essentially inactive in controlling the branching ratio of this reaction.

Laser Control of Chemical Reactions

“…Significant advances in ab initio quantum chemistry techniques are enabling potential energy surfaces to be calculated to a high accuracy for simple reactions (11). However, one problem is that reaction rate constants k(T) often depend exponentially on the height E a of the barrier in a potential energy surface according to the Arrhenius expression k(T) ϭ Aexp(ϪE a /RT), where A is a constant, R is the gas constant, and T is temperature.…”

“…Here, fast H atoms were generated by photolysis of HI, and the HOD stetching fundamental was excited by laser irradiation in the infrared. Bronikowski et al (8) ϩ was selectively prepared with excitation of its umbrella inversion mode or its all-symmetric stretching mode (11). Charge transfer is enhanced with umbrella inversion motion, and this effect has been rationalized by the preference of the neutral molecule to take on a pyramidal geometry.…”

Proton and electron transfers in O•H•O and C•H•O hydrogen-bridged ions: their role in the dissociation chemistry of ionized acetol, CH3C(=O)CH2OH•+

“…Interestingly, these are the very processes that are known to occur rapidly in hydrogen-bridged radical cations formed by direct ionization of gas phase clusters (15) (these processes also take place rapidly in ion-molecule encounters, see for example ref. 16, and indeed the proposed intermediates in eqs.…”

Fine- and hyperfine-structure effects in molecular photoionization. II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations

“…In particular, selection and propensity rules governing the REMPI process may be exploited for rotational-vibrational state-selective production of molecular cations. 3,4,[7][8][9] In the preceding article, 10 cited as Paper I below, we have presented a model for fine-structure-(fs) and hyperfinestructure-(hfs)-resolved photoionization intensities in direct, one-photon ionization of molecules. Here, we extend our model to cover two-color multiphoton ionization.…”

“…Resonance-enhanced multiphoton ionization (REMPI)-ionization of atoms or molecules by several photons via resonant excitation of the neutral precursor specieshas become a well-established method to study the photoionization of molecules 1,2 and produce molecular cations for dynamics and spectroscopy experiments [3][4][5][6] over the last decades. Multiphoton ionization avoids the need for vacuumultraviolet radiation, while resonant ionization, i.e., ionization via an excited state of the neutral precursor molecule, can increase the photoionization yield and improves the selectivity of the ionization process.…”