The tautomerization dynamics of porphycene and its isotopomers – Concerted versus stepwise mechanisms

Mode‐Selective Promotion and Isotope Effects of Concerted Double‐Hydrogen Tunneling in Porphycene Embedded in Superfluid Helium Nanodroplets

“…[4] Still, the question on the tunneling mechanism as deduced from theoretical investigations could not be confirmed by the experimental data for Pc. [5,6] Therein, the authors express the demand for more experimental data to improve and test theoretical tunneling models. Our paper provides new experimental data which have been obtained by applying a new experimental technique for the preparation of cold isolated Pc, essential conditions for studying tunneling.…”

“…[10] The nitrogen atoms, arranged in rectangular configuration, comprise four sites for two hydrogen atoms, which leads in general to six pairwise mirror-symmetric configurations, two trans and four cis, thus a rather complex tunneling system. [5,6,11,12] Scheme 1 depicts all possibilities for tautomerization among the six configurations via tunneling of the two hydrogen atoms, distinguishing between concerted (c) and stepwise (a) processes, depending on the particular tautomers involved. An additional challenge is to study the influence of additional vibrational excitation on the intramolecular double hy-drogen tunneling, never reported so far to the best of our knowledge.…”

Vibrations and hydrogen bonding in porphycene

“…There are two other modes that introduce significant perturbation to f 96 . The normal mode 2 AG (j = 7), widely discussed 18,27,35,36 in the context of the mechanism of the double proton transfer reaction in porphycene, modulates the fundamental frequency of the 30 BU mode within the range of 334 cm À1 , between 2575 cm À1 and 2910 cm À1 .…”

“…These findings point to the important role of tunneling and indicate a multidimensional character of tautomerization in porphycene, confirmed by theoretical studies. 18,24,27,[34][35][36] In a work devoted to identifying vibrational modes relevant for the proper description of the potential governing the motion of the inner protons, Ku¨hn and co-workers used four-dimensional and six-dimensional nuclear wavefunctions, the latter for a singly deuterated isotopologue. 35 Naturally, the key to understanding the complex mechanism of tautomerization in Pc is the knowledge of the intramolecular hydrogen bond (HB) parameters.…”

Path integral approach to the calculation of reaction rates for a reaction coordinate coupled to a dual harmonic bath

“…The latter fact is not surprising since the shapes of potential curves for hydrogen and deuterium transfers are the same and the only difference lies in the length of the step ∆s which appears in Eq. (9). The ratio for the steps is only slightly different from one, ∆s(H)/∆s(D) = 0.9978.…”