IR continua of hydrogen bonds and hydrogen-bonded systems, calculated proton polarizabilities and line spectra

Abstract

Homoconjugated B +H·B⇌B·H +B hydrogen bonds cause intense continua in the IR spectra. Continua are also observed in the case of heteroconjugated (I) AH·B⇌A −·H +B (II) bonds if the two proton limiting structures have noticeable weight. In this case, with the exception of extreme systems, the double minimum of the proton potentials is created by the interactions of these hydrogen bonds with their environments. Finally, structurally symmetrical or largely structurally symmetrical hydrogen-bonded chains or chains which are built up by the above mentioned hydrogen bonds cause continua by collective proton motion. Theory proves that all these three types of hydrogen bonds and hydrogen-bonded systems show so-called proton polarizabilities due to proton shifts. These proton polarizabilities are two orders of magnitude larger than usual polarizabilities due to distortion of electron systems, and with hydrogen-bonded chains they may be much larger still. The calculated line spectra of all these systems show many lines which shift as a function of the electrical field strength at the hydrogen bonds (simulating their environments). In the whole region some lines vanish, some arise with changes of the electrical field strength. The IR continua occur due to strong interaction effects of these hydrogen bonds or hydrogen-bonded systems with their environments which are caused by the large proton polarizability. Hydrogen bonds with large proton polarizability are of great significance with the electrochemistry of acid and base solutions. Furthermore, it is proved that a large number of hydrogen bonds and hydrogen-bonded systems occurring in biochemistry show large proton polarizability. Their hypothetical importance for biological functions is discussed. Finally, it is shown that at surfaces hydrogen bonds and hydrogen-bonded systems with large proton polarizability may be present and should be taken into account, when studying reactions at surfaces in which protons are involved.