Quantum-chemical study and FTIR jet spectroscopy of CHCl3–NH3 association in the gas phase

Abstract

High level ab initio quantum chemical calculations have been performed on the association of chloroform with ammonia in the gas phase (counterpoise corrected MP2 and coupled-cluster CCSD(T) calculations with 6-311++G(d,p) basis functions). Minimum energy equilibrium structures have been found for CHCl(3)-NH(3) dimer, CHCl(3)-(NH(3))(2) trimer and CHCl(3)-(NH(3))(3) tetramer. Association is characterised by a CHN hydrogen bond between a chloroform and an ammonia molecule, with further ammonia units attached by hydrogen bonds to ammonia and by an electrostatic NHCl interaction to chloroform. Cooperative effects provide additional stabilisation. The complexes exhibit characteristic shifts of vibrational bands and change of IR intensity; in particular there is a pronounced progressive shift of the CH-stretching vibration towards lower wavenumber with each unit of ammonia attached in the complex. The shift is accompanied by an up to 600 fold increase in IR intensity. The experimental FTIR jet spectra have provided firm evidence of CHCl(3)-NH(3) association, with the clearest effects seen in the region of the CH-stretching vibration. First tentative assignments have been made based on the dependence of relative intensities of cluster features on the concentration of monomers, and assignments have been corroborated by the quantum chemical calculations. The present combined ab initio and FTIR spectroscopy study reveals the structure and energetics of cluster formation and intermolecular bonding in CHCl(3)-NH(3) association.

CH⋅⋅⋅N Hydrogen‐Bonding Interaction in 7‐Azaindole:CHX3 (X=F, Cl) Complexes

“…In contrast to the CÀH···O or CÀH···p interactions, the hydrogenbond donor CÀH group in these complexes always shows a redshift in its stretching frequency. [14,15] Studies in inert gas matrices show even larger redshifts, namely, 45 cm À1 in an Ar matrix and 94 cm À1 in an N 2 matrix. The 1:1 complexes of CHCl 3 with NH 3 have been studied by IR spectroscopic methods in the gas phase.…”

“…CHCl 3 :NH 3 À45 [29] Ar matrix 20 K CHCl 3 :NH 3 À94 [29] N 2 matrix 20 K; broad peak CHCl 3 :(NH 3 ) 2 À77 [14] supersonic jet FTIR jet temp.…”

“…CHCl 3 :(NH 3 ) 3 À102 [14] supersonic jet FTIR jet temp. CHF 3 :NH 3 + 7.6 [30] liquid Xe 188 K CHF 3 :NH 3 À21 [29] Ar matrix 20 K CHF 3 :NH 3 À45 [29] N 2 matrix 20 K CHCl 3 :NMe 3 À105 [31] liquid Kr 120 K F 2 ClCH:NMe 3 À32 [31] liquid Kr 120 K CHF 3 :NMe 3 À22.8 [30] liquid Ar 90 K CDCl 3 :NH 3 À12 [32] gas-phase IR room temp.…”

“…Figure 2 b shows the FDIR spectrum corresponding to the 7-AI:CHCl 3 complex. [12,14,24] This indicates that the CÀH stretching transition of the CHCl 3 moiety in this complex is red shifted by 82 cm À1 . An intense and broad peak was observed centered at 2951 cm À1 .…”

“…[13][14][15] Vibrational spectroscopy in conjunction with molecular beams is a very powerful technique for the investigation of weakly bound size-selected clusters. There are far fewer gas-phase experimental studies, and among these the CÀH···N interactions, which are no less abundant than their CÀH···O or CÀH···p counterparts, have received very little attention.…”