Vibrationally state-selected reactions of ammonia ions. I. NH+3(v)+D2

Abstract

Resonance enhanced multiphoton ionization has been applied to the production of vibration ally state-selected ion beams. Ammonia ions are selectively formed with a specific number of vibrational quanta in the V 2 umbrella bending mode. The effect of vibrational excitation of this mode on thereactionofNH 3 + (X, v = 0 to 9) withD 2 is examined over the 0.5 to 10eV center-ofmass kinetic energy range in a tandem quadrupole mass spectrometer. Under these conditions, ( 1) abstraction of a D atom to form NH3D + is the dominant reaction channel, (2) NH3D + having sufficient internal energy may decompose to yield NH2D + and this decomposition process is enhanced by vibrational excitation of the NH3+ reagent, and (3) NH2D + is also formed by direct hydrogen--deuterium exchange of NH3+ with D 2 , but this channel appears as a minor contribution which is insensitive to the vibrational excitation of the NH3+ . A spectator stripping model is able to account for the ratio ofNH 2 D+ to NH3D+ as a function of the NH3+ translational and vibrational energy.

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.…”

Reduced dimensionality wave packet study of the NH3++H2, D2 reaction

“…[14][15][16][17] The latter reaction appears to be very efficient compared to ͑3͒: Kemper et al 14 measured a very strong increase of the NH 2 D ϩ production as the internal energy of NH 3 ϩ increases. Similarly, the group of Zare 15-17 observed a strong enhancement of the NH 2 D ϩ production when the collision energy reaches ϳ5 eV.…”

“…Yet, H and D atoms being equivalent from the molecular structure point of view, one may wonder why this mechanism does not produce NHD 2 ϩ . Notwithstanding the existence of reactions ͑3͒ and ͑5͒, the dominant process [15][16][17] at a collision energy below 5 eV is by far the reactions ͑1͒ or ͑2͒, especially when the internal energy of the ammonium ion is moderate ͑below 1 eV͒. Moreover, except at very low-collision energy, this reaction occurs through a direct process.…”

Chemistry With Controlled Ions

“…Various variants of this approach have been implemented. Vibrationally state-selected ions have been produced by resonantly ionizing via specific vibrational states of a suitable Rydberg state of the neutral precursor molecule and capitalizing on diagonal Franck-Condon factors in the ionization step [64,63,65]. Rotational state selection has been achieved 2) Note, however, that in large crystals, thermal diffusion of the ions within the crystal structure can still be observed if the temperature is not sufficiently low [56].…”