Imaging Studies of the Photodissociation of NH₃⁺ and ND₃⁺ Cations

Abstract

Velocity map ion imaging methods have been used to study the photofragmentation dynamics of state-selected NH3+ and ND3+ cations. The cations were prepared in selected nu2+ bending vibrational levels of the ground (x2A'') electronic state by two-photon resonant, three-photon ionization of NH3(ND3), via several different nu2' levels of the and ' Rydberg states. Subsequent excitation to the A2E state by absorption of a 207.6 nm photon resulted in N-H(D) bond fission and NH2+(ND2+) fragment ion formation. These fragments exhibit isotropic recoil velocity distributions, which peak at low kinetic energy but extend to the maximum allowed by energy conservation. Such findings accord with conclusions from earlier electron induced photoionization and photoelectron-photoion coincidence studies of NH3 at similar total energies (defined relative to the ground-state neutral) and, as previously, can be rationalized in terms of excitation to the Jahn-Teller distorted state, rapid radiationless transfer via one or more conical intersections linking the and state potential energy surfaces (PESs) and subsequent unimolecular decay on the latter PES. Weak NH2+ and NH+ fragment ion signals are also observed when exciting with the ionization laser only; imaging these fragment ions provides some insights into their likely formation mechanisms.

Nonadiabatic nuclear dynamics of the ammonia cation studied by surface hopping classical trajectory calculations

“…An interesting example is the photoionization of ammonia (NH 3 ) and the nonadiabatic nuclear dynamics of the ammonia cation (NH + 3 ) which for decades have been of great interest from the experimental as well the theoretical point of view, see, e.g., Refs. [5][6][7][8][9][10] and references therein.…”

“…Photoelectron spectra of ammonia corresponding to the electronic ground state, as well as the two-fold degenerate excited state of the ammonia cation have been measured, see 6,10 and references therein for experimental results. One of the interesting experimental findings is that NH + 3 ( Ã 2 E − X 2 A 1 ) fluorescence was not observed 41 , supporting the idea of fast nonradiative decay processes due to a conical intersection 42 .…”

UV photofragmentation dynamics of acetaldehyde cations prepared by single-photon VUV ionization

“…Ashfold and co-workers have used this approach to examine the photochemistry of the cations of diatomic halogens and interhalogens, [10][11][12] alkyl halides, 13 and first-row hydrides. 14,15 Suits and co-workers have examined the photochemistry of several aldehyde, [16][17][18] amine, 19,20 and alkene cations; 21,22 their work on cation photofragmentation using imaging techniques has been summarized in a mini-review. 23 Single-photon VUV ionization at 118 nm has also been used to prepare acetone cations, with photofragmentation induced by the residual 355 nm radiation used in VUV generation.…”

Photofragment imaging from mass-selected ions using a reflectron mass spectrometer. II: Formation mechanism of MgF+ in the photodissociation of Mg+FCH3 complex

“…In addition to the photodissociation of neutrals, the ion imaging measurements have been performed to observe the fragment ions produced by the photodissociation of molecular ions [17][18][19][20]. In these experiments, a mass-selected parent ion was initially generated by a resonance-enhanced multiphoton ionization (REMPI) and then dissociated into fragments by a photolysis laser.…”