UV Photodissociation of Ethylamine Cation: A Combined Experimental and Theoretical Investigation

Abstract

Direct current (DC) slice imaging of state-selected ions is combined with high-level ab initio calculations to give insight into reaction pathways, dynamics, and energetics for ethylamine cation photodissociation at 233 nm. These reaction pathways are of interest for understanding the rich chemistry of Titan's ionosphere recently revealed by the Cassini mission. The result for the H-loss product has a bimodal translational energy distribution, indicating two distinct H-loss pathways: these are assigned to triplet CH(3)CH(2)NH(+) product ions and the singlet CH(3)CHNH(2)(+) species. The distribution shows a modest fraction of energy available in translation and is consistent with barrierless dissociation from the ground state. HCNH(+) formation is observed as the dominant channel and exhibits a bimodal translational energy distribution with the faster component depicting a significant angular anisotropy. This suggests a direct excited-state decay pathway for this portion of the distribution. We have also observed the H + H(2) loss product as a minor secondary dissociation channel, which correlates well with the formation of CH(2)CNH(2)(+) ion with an exit barrier.

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

“…In mass spectrometric applications, ion fragmentation is often assumed to proceed statistically as described by the quasi-equilibrium theory (QET), in which dissociation depends only on total energy rather than the nature of the excitation. 25,26 Excited state dynamics in polyatomic cations was recently observed by Gichuhi et al, 19 who used velocity map imaging to detect HCNH + fragments formed after excitation of ethylamine cations (CH3CH2NH2 + ) at 233 nm. Two components were also observed in the ET distributions: a dominant slow component peaking at ET ≈ 0 and a minor fast component.…”

“…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.…”

“…25,26 Examples demonstrating the involvement of excited states in the fragmentation of molecular cations are few. 13,15,16,19 Information about the electronic states and energy-dependent fragmentation of CH3CHO + comes largely from photoelectron spectroscopy and photoelectron/photoion coincidence (PEPICO) measurements. He I and threshold photoelectron spectra of acetaldehyde show an intense, sharp 0-0 band near 10.29 eV, [27][28][29][30][31] indicative of ionization from the non-bonding nO (10a′) orbital.…”

Velocity map ion imaging study of Ar2+ photodissociation

“…Velocity and kinetic energy distributions may be used to study the partitioning of excess energy among the various internal degrees of freedom of the photofragments, and the nature of the electronic transition leading to photodissociation may be inferred from the angular distribution. While the field of photofragment imaging as applied to the photochemistry of neutral molecules has certainly come of age, very few ions have been studied in this way [12][13][14][15][16][17][18][19]. We have recently developed a new time-of-flight mass spectrometer for velocity-map imaging (VMI) [2] of the photofragments from mass-selected ions [19].…”

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.…”