Full dimensional (15 dimensional) quantum-dynamical simulation of the protonated water-dimer IV: Isotope effects in the infrared spectraof D D_2O)_2~+, H(D_2O)_2~+, and D(H_20)_2~+ isotopologues

摘要

The infrared spectra of H(H_2O)_2~+, D(D_H(2~+, and H_+isotopologues of the Zundelcation in the spectral range of 0-4000 cm~(-1)are computed by quantum dynamics in fulldimensionality using the multiconfiguration time-dependent Hartree method. The spectra presentdramatic isotope effects in the middle spectral region between 600 and 2000 cm~(-1). Not only theexpected line shifts due to isotopic substitution take place but the intensities of the peaks and thenumber of absorptions with appreciable intensity vary. The most complex spectrum is the one ofH(D_2O)_2~+, in which a group of at least four coupled vibrational modes is found in a narrow spectralrange between 1000 and 1500 cm~(-1)and is responsible for the three peaks found in this spectralregion. The simplest spectrum of the series corresponds to D(H_2O)_2~+. In this case deuteration of thecentral position induces decoupling of the vibrational modes, especially of the asymmetric centralproton mode and the ungerade water bending, leading to a spectrum which is easy to assign andinterpret. Zero-point energies and low energy vibrational eigenstates of each isotopologue related tothe wagging (pyramidalization) and water-water internal relative rotation are computed using theblock improved relaxation algorithm. The effect of isotopic substitution on these states is discussed.The reported simulations provide detailed information on the dynamics and vibrational spectroscopyof the Zundel cation and contribute to our general understanding of protonated water clusters and thehydrated proton.