Structure, Dynamics, and Accurate Laboratory Rotational Frequencies of the Acrylonitrile-Methanol Complex.

Camilla Calabrese,Assimo Maris,Wolf D Geppert,Pantea Fathi,Sonia Melandri,Annalisa Vigorito,Sergio Mariotti

doi:10.1021/acs.jpca.0c01334

Abstract

The hydrogen-bonded complex between acrylonitrile (CH2=CHCN) and methanol has been characterized spectroscopically in the millimeter wave range (59.6–74.4 GHz) using a free jet absorption millimeter wave spectrometer. Precise values of the rotational and centrifugal distortion constants were obtained from the measured frequencies of the complex of acrylonitrile with CH3OH and CD3OD. The analysis of the splittings of the rotational lines due to the hindered internal rotation of the methanol methyl group led to the determination of a V3 value of 221.9(7) and 218(5) cm–1 for the complexes of CH3OH and CD3OD, respectively, and these values are about 40% lower than that of free methanol. The structure of the observed conformation is in agreement with the global minimum determined at the MP2/aug-cc-pVTZ level of calculation, and the counterpoise corrected intermolecular binding energy, obtained at the same theoretical level, is De = 26.3 kJ mol–1.

Highlights

Hydrogen-bonded clusters have been in the constant focus of interest of theoretical and experimental chemists
This paper presents a microwave spectroscopy study of the 1:1 ACN·Met cluster in the region between 59.6 and 74.4 GHz
The conformational space of ACN·Met was explored running several ab initio optimization procedures, each of them starting from a different initial geometry

Summary

Introduction

Hydrogen-bonded clusters have been in the constant focus of interest of theoretical and experimental chemists. Despite the noncovalent character of the hydrogen bond (HB), they can be quite stable, and hydrogen-bonded species (especially water clusters) have been found in a multitude of environments including planetary atmospheres. Hydrogen-bonded water clusters can act as templates for formation of larger entities. This way, large water clusters of both cations and anions can be formed, which appear downward from the D-layer of the terrestrial ionosphere (60−100 km altitude). Some classes of molecules (e.g., alcohols, acids, amides) are very prone to HB formation, acting either as a proton donor or acceptor. Clusters of acrylonitrile (CH2 CHCN, on denoted as ACN) with water and alcohols are readily formed and could even exist in the interstellar medium and atmospheres of other planets and satellites. Clusters of interstellar molecules with water and methanol, appear to be very promising targets of observations, especially in starforming regions where the warm-up during star formation leads to evaporation of the icy mantles of the interstellar grains that contain considerable amounts of these two compounds

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