Theoretical investigations of proton and hydrogen atom transfer in the condensed phase (original) (raw)
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A dynamical theory of nonadiabatic proton and hydrogen atom transfer reaction rates in solution
A dynamical theory for the rate constant k of hydrogen atom and proton transfer reactions in solution is presented for the nonadiabatic limit, where reaction is dominated by tunneling. Coupling and splitting fluctuation effects arising from intramolecular vibrational and solvent fluctuations are included in the description. Limiting regime analytic results fork are presented for high and low temperature and for weak and strong salvation. Differences between proton and hydrogen atom transfers are indicated, as are the contrasts with electron transfer rates.
A simple model for proton transfer
Chemical Physics, 1995
A simple model is presented for the study of proton transfer in hydrogen bonds. The energetics and dynamics of a simplified unidimensional proton coordinate under the presence of an effective potential is considered. The transfer of a proton from one nucleus to another depends on the effective potential at each site and the coupling between the two electronic states. The model describes these features with three factors: the geometry of the system, the non-bonding interaction, and the electronic coupling strength. The validity of a two level approximation for proton transfer is considered. The transition from a two level to a nontwo level system is dependent on the effective hydrogen bond length R used, the electronic coupling TAB, and the non-bonding interaction strength represented by A u. For a reasonable range of TAn (0.5-2.5 eV) and A u (350-550 cm 1) the transition occurs for R = 2.6-2.9 &. The application of the model to realistic systems is discussed.
Chemical Physics Letters
A review of the proton transfer reactions (PTR) of model base pairs such as the 7-azaindole and 1azacarbazole dimers is presented, including some of the recent progress in the laser spectroscopy of these dimers. Advances in computational chemistry now allow to calculate reliable potential energy surfaces of the excited-state PTR, which is indispensable to understand the experimental results. The comprehensive results on the spectroscopy and reactivity of these dimers are outlined for fully explaining the excited state PTR of model base pairs on the basis of the current theoretical studies. Moreover, the recent studies on the PTR in the ground state relating to a back proton translocation of tautomeric dimer of 7-azaindole are presented. Finally, the outlook on the study of the PTR of model base pairs is addressed to further explore the reaction dynamics of these benchmark systems.
Mechanisms of Double Proton Transfer. Theory and Applications
Zeitschrift für Physikalische Chemie, 2008
An analytical two-dimensional (2D) potential-energy surface based on two equal hydrogen bonds coupled by a correlation term, recently introduced [J. Chem. Phys. 127 (2007) 174513] to describe the dynamics of double proton transfer, is reviewed and generalized. It is then applied to the evaluation of proton transfer dynamics in a number of realistic systems, namely several molecules and dimers that exhibit various degrees of correlation between the motions of the two protons. The three parameters required to generate this 2D potential are derived from electronic structure and force field calculations, such that they include implicitly the effect of coupled skeletal modes. It follows that explicit introduction of such coupled modes is not required to obtain the basic relations that define the stationary points of the 2D surface, and thereby the reaction mechanism. Based on these relations, a detailed analysis is reported of a variety of systems exhibiting double proton transfer, inclu...
1996
Using ab initio direct dynamics, selected reaction trajectories were calculated for the title reaction. The lifetime of the intermediate ion-molecule complex formed upon encounter of the reactants depends strongly on their initial relative orientation. When the proton to be transferred is properly lined up between the oxygen and the nitrogen, rapid transfer is observed. This leads to deposition of a high and nonstatistical fraction of the reaction enthalpy into the product ammonium ion. Less favorable initial orientations appear to give a more statistical distribution of the energy. A strong basis set dependence of the dynamics is observed. It is concluded that moderately large basis functions including polarization functions should be used for future dynamical studies. Alternatively, precise analytical surfaces may be used. Dynamics Calculations of H 3 O + + NH 3 f NH 4 + + H 2 O
The Journal of Physical Chemistry, 1995
Using ab initio direct dynamics, selected reaction trajectories were calculated for the title reaction. The lifetime of the intermediate ion-molecule complex formed upon encounter of the reactants depends strongly on their initial relative orientation. When the proton to be transferred is properly lined up between the oxygen and the nitrogen, rapid transfer is observed. This leads to deposition of a high and nonstatistical fraction of the reaction enthalpy into the product ammonium ion. Less favorable initial orientations appear to give a more statistical distribution of the energy. A strong basis set dependence of the dynamics is observed. It is concluded that moderately large basis functions including polarization functions should be used for future dynamical studies. Alternatively, precise analytical surfaces may be used. Dynamics Calculations of H 3 O + + NH 3 f NH 4 + + H 2 O
2009
The excited-state intramolecular proton transfer (ESIPT) is reviewed for several benchmark systems [o-hydroxybenzaldehyde (OHBA), salicylic acid and 2-(2′-hydroxyphenyl)-benzothiazole (HBT)] in order to verify the applicability of the time-dependent density functional theory (TDDFT) and the resolution-of-the-identity approximate second-order coupled cluster (RI-CC2) methods. It was found that these approaches are very well suited for the description of ESIPT processes. A comparative investigation of previous and new excited-state dynamics simulations is performed for HBT, 10-hydroxybenzo[h]quinoline (HBQ), and [2,2′-bipyridyl]-3,3′-diol (BP(OH)2). The time scale for the ESIPT process in these systems ranges in the time interval of 30−40 fs for HBT and HBQ and amounts to about 10 fs for the first proton transfer step in BP(OH)2. The dynamics simulations also show that the proton transfer in HBT is strongly supported by skeletal modes and the proton plays a rather passive role, whereas in HBQ a semipassive mechanism is found due to its increased rigidity in comparison to HBT. The special role of the double proton transfer in BP(OH)2 is discussed as well.