located closer to one of the NH 3 moiety with a C 3v geometry. Furthermore, the
proton transfer coordinate is described by a double well potential as it traverses
between two nitrogen atoms.
On the other hand, classical Monte Carlo approach and wavepacket dynamics
under MP2/6-31+G* simulations were reported by Asada et al. [16]. Optimized
structures and transition state geometries were found to be C 3v and D 3d respectively.
Classical ab initio Monte Carlo reveals that the C 3v structure is a consequence of
classical considerations. However, once quantum effects on the proton kinetics had
been accounted, the structure was found to be D 3d .
Variational calculations were done by Yang [17–19] on protonated ammonia
cluster, NH 4
+ (NH 3 ) n for n = 1–4 under MP2 level of theory. For NH 4
+ (NH 3 ), local
mode calculations were reported up to six degrees of freedom. Isotope studies were
also performed. Based from their results, six dimensional treatment is sufficient to
describe the experimental IR spectrum, which previous theoretical treatments failed
to account.
One straightforward quantum treatment of all nuclear degree of freedom is using
Path Integral Molecular Dynamics, PIMD. The study of protonated ammonia dimer
(NH 3 ) 2 H
+ has been done by Ishibashi et al. [20]. Geometric isotope effect is discussed at 300 K with imaginary time slice P = 16. Propagation along Born–
Oppenheimer surface is at MP2 level with 6-31++G** basis set during the MD
sampling. Statistical properties depending only on 3N coordinate space could be
directly estimated. Two internal coordinates, N–N bond distance and antisymmetric
N–H bond stretching, are found essential for nuclear quantum effect to illustrate the
geometric difference between H and D.
The aim of this study is to consider the behavior of the shared proton sandwiched between amines with varying degrees of methylation. The stratagem was by
means of changing the degree of methylation, the potential energy surface can be
tuned as well as the corresponding vibrational frequencies. This in turn can help in
understanding and interpreting the spectrum where the shared proton is under a tug
of war between molecules with the same proton affinities.
2 Calculation Methods
In this work, we use a combination of several theoretical methods to account for the
quantum nature of the shared proton. First, the interactions among the nuclei are
described by ab initio methods. Second, full dimensional quantum treatment of
nuclear degrees of freedom using Path Integral Molecular Dynamics (PIMD)
method were carried out to extract key degrees of freedom associated with proton
motion. Vibrational Hamiltonian on selected dimensions were constructed to
compute spectroscopic features.
Proton Quantum Confinement on Symmetric …
79
proton transfer coordinate is described by a double well potential as it traverses
between two nitrogen atoms.
On the other hand, classical Monte Carlo approach and wavepacket dynamics
under MP2/6-31+G* simulations were reported by Asada et al. [16]. Optimized
structures and transition state geometries were found to be C 3v and D 3d respectively.
Classical ab initio Monte Carlo reveals that the C 3v structure is a consequence of
classical considerations. However, once quantum effects on the proton kinetics had
been accounted, the structure was found to be D 3d .
Variational calculations were done by Yang [17–19] on protonated ammonia
cluster, NH 4
+ (NH 3 ) n for n = 1–4 under MP2 level of theory. For NH 4
+ (NH 3 ), local
mode calculations were reported up to six degrees of freedom. Isotope studies were
also performed. Based from their results, six dimensional treatment is sufficient to
describe the experimental IR spectrum, which previous theoretical treatments failed
to account.
One straightforward quantum treatment of all nuclear degree of freedom is using
Path Integral Molecular Dynamics, PIMD. The study of protonated ammonia dimer
(NH 3 ) 2 H
+ has been done by Ishibashi et al. [20]. Geometric isotope effect is discussed at 300 K with imaginary time slice P = 16. Propagation along Born–
Oppenheimer surface is at MP2 level with 6-31++G** basis set during the MD
sampling. Statistical properties depending only on 3N coordinate space could be
directly estimated. Two internal coordinates, N–N bond distance and antisymmetric
N–H bond stretching, are found essential for nuclear quantum effect to illustrate the
geometric difference between H and D.
The aim of this study is to consider the behavior of the shared proton sandwiched between amines with varying degrees of methylation. The stratagem was by
means of changing the degree of methylation, the potential energy surface can be
tuned as well as the corresponding vibrational frequencies. This in turn can help in
understanding and interpreting the spectrum where the shared proton is under a tug
of war between molecules with the same proton affinities.
2 Calculation Methods
In this work, we use a combination of several theoretical methods to account for the
quantum nature of the shared proton. First, the interactions among the nuclei are
described by ab initio methods. Second, full dimensional quantum treatment of
nuclear degrees of freedom using Path Integral Molecular Dynamics (PIMD)
method were carried out to extract key degrees of freedom associated with proton
motion. Vibrational Hamiltonian on selected dimensions were constructed to
compute spectroscopic features.
Proton Quantum Confinement on Symmetric …
79