Structures and stability of hydrated clusters of hydrogen chloride, HCl(H2O)n, n=1–5

Abstract

The molecular structures of the hydrated clusters of the HCl molecule, HCl(H2O)n, n=1–5, are examined by employing density functional molecular orbital methods. The most stable structures of the n=1–3 clusters are found to be of the proton nontransferred type. In the case of the n=4 cluster, the proton nontransferred and proton transferred structures have nearly similar energies. There are several stable isomers for the n=5 case and the structures of these isomers are found to be all proton transferred. The relative stabilities of the direct ion-pair H+Cl−(H2O)n and the indirect ion-pair H3O+(H2O)n−1Cl− are discussed in conjunction with their structures. The prediction of the IR spectra of the stable HCl(H2O)n clusters clearly indicate the large red-shifts of the H–Cl stretching and hydrogen-bonded O–H stretching frequencies.

Finite-Temperature Effects on the Stability and Infrared Spectra of HCl(H2O)6 Clusters

“…18 Re et al found that proton transfer in the hydrogen-bonded cluster HCl(H 2 O) n with n ) 1-5 completely occurs only in the case of n ) 5 clusters. 19 Using the B3LYP density functional method and the CCSD(T) ab initio method, Milet et al showed however that HCl starts dissociating already in HCl(H 2 O) 4 . 20 Devlin et al, using ab initio Monte Carlo simulations found that in HCl-(H 2 O) 6 three-coordinated HCl dissociates directly to form a clearly recognizable solvated Cl -and H 3 O + ion pair.…”

Characterization of gas-phase HCl-H 2 O clusters using pulsed infrared cavity ringdown spectroscopy

“…HCl(H 2 O) n and (H 2 O) n+1 clusters have similar structure and hydrogen bond strengths up to at least n = 3, after which dissociation of the acid into the ion pair is predicted to occur for the acid clusters 3,7 . The similar structures and hydrogen bond strengths of the acid and pure water clusters gives rise to similar vibrational modes.…”

“…At the MP2/6-31g(2dp) level the HCl bond length increases from the isolated molecule by 1.3% upon forming the dimer, 2.5 % for the two water cluster and 4.1% for the three water cluster . By the addition of a fourth water, the dissociated ion pair becomes the most stable product according to theory 3,7 .…”

Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

“…One inquiry that persistently threads its way through this subject is: what is the minimum quantity of water molecules, (H 2 O) n , required to dissociate the acid [18]? According to calculations, the acidically dissociated structure is supported starting from n=4; most of the theoretical approaches agree that at this size the dissociated form represents the global minimum on the potential energy surface [18][19][20][21][22][23][24]. Experimentally, for neutral clusters the question has been probed by laser spectroscopy (see, e.g., [25][26][27][28]) but finding a conclusive spectroscopic signature of the onset of dissociation in a nanocluster is not straightforward.…”