Ultrafast Hydrogen Transfer in N, N-Dimethylisopropyl Amine Clusters (original) (raw)
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Structural dynamics and energy flow in Rydberg-excited clusters of N,N-dimethylisopropylamine
The Journal of Chemical Physics, 2011
In molecular beams, the tertiary amine N,N-dimethylisopropyl amine can form molecular clusters that are evident in photoelectron and mass spectra obtained upon resonant multiphoton ionization via the 3p and 3s Rydberg states. By delaying the ionization pulse from the excitation pulse we follow, in time, the ultrafast energy relaxation dynamics of the 3p to 3s internal conversion and the ensuing cluster evaporation, proton transfer, and structural dynamics. While evaporation of the cluster occurs in the 3s Rydberg state, proton transfer dominates on the ion surface. The mass-spectrum shows protonated species that arise from a proton transfer from the alpha-carbon of the neutral parent molecule to the N-atom of its ionized partner in the dimer. DFT calculations support the proton transfer mechanism between tightly bonded cluster components. The photoelectron spectrum shows broad peaks, ascribed to molecular clusters, which have an instantaneous shift of about 0.5 eV toward lower binding energies. That shift is attributed to the charge redistribution associated with the induced dipoles in surrounding cluster molecules. A time-dependent shift that decreases the Rydberg electron binding energy by a further 0.4 eV arises from the structural reorganization of the cluster solvent molecules as they react to the sudden creation of a charge.
2021
The ability of phenol to transfer the proton to surrounding ammonia molecules in a phenol-(ammonia)n cluster will depend on the relative orientation of the ammonia molecules and a critical field of about 285 MV cm-1 is essential along the O–H bond for the transfer process. Ab-initio MD simulations reveal that for a spontaneous proton transfer process, the phenol molecule must be embedded in a cluster consisting of at least eight ammonia molecules, even though several local minima with proton transferred can be observed for clusters consisting of 5-7 ammonia molecules. Further, phenol solvated in large clusters of ammonia, the proton transfer is spontaneous with the proton transfer event being instantaneous (about 20-120 fs). These simulations indicate that the rate-determining step for the proton transfer process is the organization of the solvent around the OH group and the proton transfer process in phenol-(ammonia)n clusters follows a curvilinear path which includes the O–H bond ...
DFT study of ground state proton transfer in 2-pyridone/2-hydroxypyridine–ammonia clusters
Chemical Physics, 2005
DFT calculations in the ground state have been performed for 2-hydroxypyridine–ammonia clusters 2HP · (NH3)n (n = 1 to 5) and their tautomers. Structures, relative energies and vibrational frequencies of these species were obtained at the B3LYP/6-31++G** level of theory. It was found that some structural parameters such as intra- and intermolecular distances and vibrational frequencies of O–H and N–H stretching, serve as probes and indicators of proton transfer in these clusters. The study of neutral forms shows that intermolecular proton transfer to the (NH3)n occurs for n = 4 and 5 in enol and keto clusters, respectively. For enol form, ion-pair cluster calculated for n = 4 is less stable than the neutral form by 7.1 kJ/mol. While, for keto form, it is calculated to be 25.4 kJ/mol less stable than the neutral form.
Physical Chemistry Chemical Physics, 2011
The photodissociation dynamics of pyrrole-ammonia clusters (PyHÁ(NH 3 ) n , n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH 4 (NH 3 ) nÀ1 products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (B0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment.
Electron transfer collisions between small water clusters and laser-excited Rydberg atoms
The Journal of Chemical Physics, 1991
The Letters to the Editor section is divided into four categories entitled Communications, Notes, Comments, and Errata. Communications are limited to three and one halfjournal pages, and Notes, Comments, and Errata are limited to one and three-fourths journal pages as described in the Announcement in the I July 1991 issue.
Chemical Physics Letters, 1998
Ž. Ž. Model studies have been made of the non-transferred reactant and proton-transferred product species of the Ž. ground-state hydrogen-bonded clusters ROH. .. NH , where ROH is an aromatic alcohol. The structure, relative energies 3 5 and vibrational frequencies of this species were obtained at the HFr6-31G) level of theory. It was found that proton transfer can proceed in the case of phenols with the electron-withdrawing substituents. A low-frequency vibration, which corresponds to the synchronous motion of the solvation shell, does exist in these clusters. The energy of the lowest pp) transition is calculated for aromatic alcohols and their anions at the CASPT2 level with a VDZ basis set.
Journal of Physical Organic Chemistry, 2010
Arrhenius curves of selected hydrogen transfer reactions in organic molecules and enzymes are reviewed with the focus on systems exhibiting temperature‐independent kinetic isotope effects. The latter can be rationalized in terms of a ‘pre‐tunneling state’ which is formed from the reactants by heavy atom motions and which represents a suitable molecular configuration for tunneling to occur. Within the Bell–Limbach tunneling model, formation of the pre‐tunneling state dominates the Arrhenius curves of the H and the D transfer even at higher temperatures if a large energy Em is required to reach the pre‐tunneling state. Tunneling from higher vibrational levels and the over‐barrier reaction via the transition state which lead to temperature‐dependent kinetic isotope effects dominate the Arrhenius curves only if Em is small compared to the energy of the transition state. Using published data on several hydrogen transfer systems, the type of motions leading to the pre‐tunneling state is e...
Preparation and characterization of long-lived molecular Rydberg states: Application to HD
The Journal of Chemical Physics, 1996
The decay dynamics by predissociation and rotational autoionization of high Rydberg states of HD close to the first few rotational levels of the ground vibronic state of the HD ϩ cation have been studied by delayed pulsed field ionization following resonant ͑1ϩ1Ј͒ two-photon absorption via the B state. Although predissociation and autoionization both contribute to the rapid decay of Rydberg states with principal quantum number nӶ100, the highest Rydberg states ͑nϾ100͒ are stable for more than 20 s. In contrast to H 2 , channels associated with an HD ϩ ͑v ϩ ϭ0, N ϩ ϭeven͒ ion core are coupled to channels associated with an HD ϩ ͑v ϩ ϭ0, N ϩ ϭodd͒ ion core. We demonstrate that complex resonances that arise from rotational channel interactions between low ͑nϳ25͒ Rydberg states characterized by a core with rotational angular momentum quantum number N ϩ ϩ2 and the pseudocontinuum of very high Rydberg states characterized by an N ϩ core can be used with high efficiency to produce long-lived high Rydberg states. An investigation of the pulsed field ionization characteristics of these complex resonances enables us to measure the branching between diabatic and adiabatic field ionization and to determine the optimal conditions required to extend the method of H-photofragment Rydberg translational spectroscopy pioneered by Schnieder et al. ͓J. Chem. Phys. 92, 7027 ͑1990͔͒ to molecular species.