INFLUENCE OF THE HYDROGEN BONDING ON THE ULTRAVIOLET SPECTRA OF ORGANIC MOLECULES AN ELECTRONIC THEORY

Author Institution: Centre de M\'ecanique Ondulatiore Appliqu\'ee“An electronic theory in presented explaining the influent of a hydrogen bond on the ultraviolet spectra of organic molecules. The complexes formed by hydrogen bonds are considered as separate units independently of the rest of the solvent molecules and are treated, for a number of molecules, by the Pariser-Parr-Pople procedure. The conclusions which can be drawn from this study are the following ones: a) The perturbations caused by a hydrogen bond on the $n \rightarrow \pi^{*}$ and $\pi \rightarrow \pi^{*}$ bands are due, essentially, to the transfer of the $\sigma$-electrons resulting from the hydrogen bond formation. In spit of the fact that this perturbation acts in a very different way in proton donor and in proton acceptor molecules, the calculated shifts of the $\pi \rightarrow \pi^{*}$ bands are bathochromic in both cases. b) These perturbations are essentially of an inductive type. It is therefore useful to compare the influence of a hydrogen bond to that of a weak inductive substituent. c) The configuration interaction effects are important in many cases.

On the Rate Constant for the Association Reaction H + CN + Ar → HCN + Ar

The importance of the chaperon mechanism (via ArCN or ArH complex formation) is investigated for the title reaction. All calculations employ the classical trajectory method to obtain the reactive cross sections while the equilibrium constants are estimated from statistical mechanics. A detailed analysis of the various approximations to the equilibrium constant is presented. Exploratory calculations based on the energy transfer mechanism are also reported. In addition, the decay rates of the HCN* and ArCN* species are examined in order to get insight on the detailed microscopic molecular dynamics. The chaperon mechanism is found to be important only at low temperatures, while the energy-transfer mechanism dominates for moderate and high ones