Matrix Isolation and ab initio study of the noncovalent complexes between formamide and acetylene.
Matrix isolation spectroscopy in combination with ab initio calculations is a powerful technique for the identification of weakly bound intermolecular complexes. Here, weak complexes between formamide and acetylene are studied, and three 1:1 complexes with binding energies of -2.96, -2.46, and -1.79 kcal/mol have been found at the MP2 level of theory (MP2/cc-pVTZ + ZPE + BSSE). The two most stable dimers A and B are identified in argon and nitrogen matrices by comparison between the experimental and calculated infrared frequencies. Both complexes are stabilized by the formamide C=O...HC acetylene and H...pi interactions. Large shifts have been observed experimentally for the C-H stretching vibrations of the acetylene molecule, in very good agreement with the calculated values. Eight 1:2 FMA-acetylene trimers (T-A to T-H) with binding energies between -5.44 and -2.62 kcal/mol (MP2/aug-cc-pVDZ + ZPE + BSSE) were calculated. The two most stable trimers T-A and T-B are very close in energy and have similar infrared spectra. Several weak bands that are in agreement with the calculated frequencies of the trimers T-A and T-B are observed under matrix isolation conditions. However, the differences are too small for a definitive assignment.
Mardyukov
Artur
A
Lehrstuhl für Organische Chemie II der Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Sánchez-García
Elsa
E
Sander
Wolfram
W
D000114:Acetylene / Q000737:chemistry*; D019281:Dimerization; D005559:Formamides / Q000737:chemistry*; D006860:Hydrogen Bonding; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D014732:Vibration
D005559:Formamides; C031066:formamide; D000114:Acetylene