DFT study on cooperativity in the interactions of hydrazoic acid clusters

Abstract

Abstract Density functional theory at the B3LYP level with the 6‐311G** basis set is performed to calculate the systems consisting of up to four hydrazoic acid molecules. The dimers are found to exhibit cyclic and chain structures with N … H contacts at ca. 2.1–2.7 Å. However, there are only cyclic structures with N … H contacts at ca. 2.0–2.3 Å and 2.0–2.1 Å in the trimer and tetramer, respectively. Hydrogen bond distances in the trimer and tetramer are shorter than those in the cyclic dimer as a result of the stronger interaction between molecules. The contribution of cooperative effect to the interaction energy is significant. After the correction of the basis set superposition error and zero‐point energy, the binding energies are −10.69, −29.34, and −54.26 kJ·mol −1 for the most stable dimer, trimer, and tetramer, respectively. The calculated IR shifts for NH stretching mode increase with the size of the cluster growths, reaching more than 200 cm −1 in the tetramer. For the most stable clusters, the transition from the monomer to dimer, dimer to trimer, and trimer to tetramer involve changes of −14.40, −25.68, and −31.88 kJ·mol −1 for the enthalpies at 298.15 K and 1atm, respectively. We also perform Mulliken populations analysis and find the Mulliken populations on intermolecular N … H increasing in the sequence of the dimer, trimer, and tetramer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 279–286, 2003