Isotope effect of hydrated clusters of hydrogen chloride, HCl(H2O)(n) and DCl(H2O)(n) (n = 0-4): application of dynamic extended molecular orbital method

The recently proposed dynamic extended molecular orbital (DEMO) method is a pplied to the HCl(H2O)(n) and DCl(H2O)(n) (n = 0-4) clusters in order to ex plore the isotope effect on their structures, wavefunctions, and energies, theoretically. Since the DEMO method determines both electronic and nuclear wavefunctions simultaneously by optimizing all parameters including basis sets and their centres variationally, we can get the different nuclear orbi tals for proton and deuteron as well as their electronic wavefunctions. The positions of the centres of nuclear orbitals show that the deuteron has we aker hydrogen bonding than the proton. There are three isomers in the case of n = 3 clusters, and less stable isomers have hydrogen transferred and no n-transferred structures. In the conventional MO calculation, both hydrogen transferred and non-transferred isomers are calculated to be energy minima . When we have applied the DEMO method, only the hydrogen transferred struc ture is obtained for HCl(H2O)(3), while both structures are optimized for D Cl(H2O)(3). Such strong H/D dependence on the structures of the HCl(H2O)(n) , and DCl(H2O)(n) clusters can be expressed directly by using the DEMO meth od. The present application demonstrates that the DEMO method is a useful t ool for analysing the anharmonicity and vibronic effects of a hydrogen bond ing system.