Vibrational dynamics of the ${\rm H}_5^+$H5+ and its isotopologues from multiconfiguration time-dependent Hartree calculations

Abstract

(2010)]. The potential energy operators are constructed using the n-mode representation adapted to a four-combined mode cluster expansion, including up to seven-dimensional grids, chosen adequately to take advantage in representing the MCTDH wavefunction. An error analysis is performed to quantify the convergence of the potential expansion to reproduce the reference surfaces at the energies of interest. An extensive analysis of the vibrational ground state properties of these isotopes and comparison with the reference diffusion Monte Carlo results by Acioli et al. [J. Chem. Phys. 128, 104318 (2008)] are presented. It is found that these systems are highly delocalized, interconverting between equivalent minima through rotation and internal proton transfer motions even at their vibrational ground state. Isotopic substitution affects the zero-point energy and structure, showing preference in the arrangements of the H and D within the mixed clusters, and the most stable conformers of each isotopomer are the ones with the H in the central position. Vibrational excited states are also computed and by comparing the energies and structures predicted from the two surfaces, the effect of the potential topology on them is discussed.

The role of large-amplitude motions in the spectroscopy and dynamics of ${\rm H}_5^+$H5+

“…This is comparable to the bending frequencies reported in the same MCTDH study of 831.1 cm −1 or 834.7 cm −1 . 17 This agreement in frequencies provides further validation of the adiabatic approach.…”

“…This agrees with the torsion frequency (92.6 cm −1 ) from a multi-configuration timedependent Hartree (MCTDH) calculation. 17 In the case of the m H 2 = 0 level, the E 0 value is 958 cm −1 higher than the E 0 obtained using the ground state potential. This is comparable to the bending frequencies reported in the same MCTDH study of 831.1 cm −1 or 834.7 cm −1 .…”

“…The proton delocalization is reflected in the low frequency of this vibrational mode as has been seen in both experimental and a variety of theoretical studies of the vibrational spectrum of H + 5 . 11,[13][14][15][16][17][18][19][20] In a recent study, we demonstrated that this proton hopping vibration is strongly coupled to the dissociation coordinate in H + 5 . 14 The third process is more complicated than the first two.…”

“…This set of Jacobi coordinates provides a more separable description of the molecular wave function near the equilibrium configuration of H + 5 , but is not as effective for describing the ion as it dissociates. This choice of coordinates has been employed in many of the studies on H + 5 of Prosmiti and co-workers 16,17,19,20 as well as by Fàbri et al 34 In the second set of Jacobi coordinates, the dissociation coordinate S is defined as the vector that connects H 2 and H + 3 , and the remaining coordinates are designated by s i . Such coordinates were used by Song et al 18 and provide a more appropriate description of H + 5 as it dissociates.…”

Rotation/Torsion Coupling in H5+, D5+, H4D+, and HD4+ Using Diffusion Monte Carlo

“…We also compare our results to those obtained from multiconfigurational time-dependent Hartree (MCTDH) calculations, 31 vibrational configuration interaction (VCI) calculations obtained using the reaction path version of MULTIMODE, 32 and full CI (FCI) calculations. 33 We believe that the 33 cm −1 shift in the zero-point energy calculated using the basis set DMC approach reflects an incomplete treatment of the coupling between the torsion and the other vibrational degrees of freedom.…”