RESUMO
This study examines the structures, energies, and IR vibrational spectra of the sulfur dioxide-water SO2(H2O) complexes by employing coupled cluster theory CCSD(T) with Dunning style correlation consistent type basis sets aug-cc-pV(n+d)Z (n = D, T, Q, 5). Complete basis set (CBS) extrapolations have been carried out to predict binding energies for two isomers of the SO2(H2O) complex: a stacked global minimum (1A) structure and a hydrogen-bonded local minimum (1B) structure. The CCSD(T)/CBS extrapolation predicts an intermolecular S-O distance rSâ¯O = 2.827 Å for the stacked isomer, which is in excellent agreement with an experimental measurement of 2.824 Å [K. Matsumura et al., J. Chem. Phys., 91, 5887 (1989)]. The CCSD(T)/CBS binding energy for the stacked dimer 1A and hydrogen-bonded form 1B is De = -4.37 kcal/mol and De = -2.40 kcal/mol, respectively. This study also employs anharmonic VPT2 MP2/aug-cc-pV(n+d)Z level corrections to CCSD(T)/aug-cc-pV(n+d)Z vibrational frequencies in both forms of SO2(H2O). The anharmonic CCSD(T)/aug-cc-pV(Q+d)Z OH stretching frequencies in the stacked structure 1A are 3743 cm-1 (ν3) and 3647 cm-1 (ν1), and these align well with the recorded IR spectroscopic values of 3745 and 3643 cm-1, respectively [C. Wang et al., J. Phys. Chem. Lett., 13, 5654 (2022)]. If we combine CCSD(T)/aug-cc-pV(n+d)Z De values with VPT2 vibrational frequencies, we obtain a new CCSD(T)/aug-cc-pV(Q+d)Z anharmonic dissociation energy D0 = -3.48 kcal/mol for 1A and D0 = -1.74 kcal/mol for 1B. In summary, the results presented here demonstrate that the application of CCSD(T) calculations with aug-cc-pV(n+d)Z basis sets and CBS extrapolations is critical in probing the structure and IR spectroscopic properties of the sulfur dioxide-water complex.
RESUMO
Ozone-water complexes O3(H2O)n (n = 1-2) have been studied using coupled cluster theory with triple excitations CCSD(T) with correlation consistent basis sets aug-cc-pVnZ (n = D, T, Q) and complete basis set (CBS) extrapolation techniques. We identified seven dimer (n = 1) and nine trimer species (n = 2) with open C2v and cyclic D3h ozone. Calculations at the CCSD(T)/CBS level of theory for C2v O3(H2O) on the counterpoise (CP)-corrected potential energy surface yield a dissociation energy of De = 2.31 kcal/mol and an O3 central-oxygen (Oc) H2O oxygen (Ow) distance r[Ocâ¯Ow] of 3.097 Å, which is in good agreement with an experimental value of 2.957 Å [J. Z. Gillies et al., J. Mol. Spectrosc. 146, 493 (1991)]. Combining our CCSD(T)/CBS value of De for C2v O3(H2O) with our best estimate anharmonic CCSD(T)/aVTZ ΔZPE yields a Do value of 1.82 kcal/mol; the CCSD(T)/CBS value of De for D3h O3(H2O) is 1.51 kcal/mol and yields an anharmonic CCSD(T)/aVTZ Do = 0.99 kcal/mol. CCSD(T)/aVTZ dissociation energies and structures for C2v O3(H2O)2 are De = 4.15 kcal/mol, (Do = 3.08 kcal/mol) and r[Ocâ¯Ow] = 2.973 Å, and De = 2.64 kcal/mol (Do = 1.68 kcal/mol) with r[Ocâ¯Ow] = 2.828 Å for D3h O3(H2O)2. The results from ab initio molecular dynamics simulations, which consider dynamic and thermal effects in O3(H2O), show that the O3(H2O) complex remains stable at 50 K and dynamically interconverts between two hydrogen-bonded conformers with short Ocâ¯Ow contacts (3.85 Å). Carr-Parrinello molecular dynamic (CPMD) simulations for O3(H2O) and O3(H2O)2 at 100 K demonstrate that O3(H2O)2 remains structurally intact, whereas O3(H2O) dissociates to free ozone and water, a feature consistent with the larger average binding energy in O3(H2O)2 (2.2 kcal/mol) vs that in O3(H2O) (1.8 kcal/mol). Finally, the results from CCSD(T)/CBS and CPMD simulations demonstrate that the large inter-trimer binding energies in O3(H2O)2 would give rise to an elevated trimer/dimer population ratio, making O3(H2O)2 a particularly stable and spectroscopically detectable complex.