DCl–H₂O, HCl–D₂O, and DCl–D₂O Dimers: Inter- and Intramolecular Vibrational States and Frequency Shifts from Fully Coupled Quantum Calculations on a Full-Dimensional Neural Network Potential Energy Surface

Abstract

We report full-dimensional and fully coupled quantum calculations of the inter-and intramolecular vibrational states of three isotopologues of the hydrogen chloride−water dimer: DCl−H 2 O (DH), HCl−D 2 O (HD), and DCl−D 2 O (DD). The present study extends our recent theoretical investigation of the nine-dimensional (9D) vibrational level structure of the HCl− H 2 O (HH) dimer [

Transfer learned potential energy surfaces: accurate anharmonic vibrational dynamics and dissociation energies for the formic acid monomer and dimer

“… 112 Similarly, NN-based energy functions have been used for accurate spectroscopic studies of van der Waals complexes such as HCl–H 2 O and its isotopologues. 113 Finally, NN-based energy functions have also been used for bond-forming/bond-breaking processes. 67,114 These developments together with suitable embedding in surrounding environments provide considerable scope to more quantitatively characterize challenging problems in physical chemistry at molecular-level detail.…”

Noncovalently bound molecular complexes beyond diatom–diatom systems: full-dimensional, fully coupled quantum calculations of rovibrational states

“…25, denoted hereafter as paper I, in which this computational methodology was applied to H 2 O/D 2 O–CO complexes. In fact, all of its applications so far have been to the water-containing triatom–diatom complexes, 17,25,36–38 the choices being dictated by the available 9D PESs. Therefore, for simplicity, in the following it will be assumed that the triatomic moiety is water.…”

“…25,36 However, this choice is not optimal for HB complexes where inter-monomer interaction is stronger. Therefore, in the case of the HCl–H 2 O complex and isotopologues 17,37,38 the 1D HCl dimer-adapted vibrational Hamiltonian was defined as Ĥ B v ( r B ) = T̂ B v ( r B ) + V B DA ( r B ).Here, V B DA ( r B ) ≡ V ( Q 0 , q 0 A , r B ). Q 0 values correspond closely to the vibrationally averaged geometry of the ground state of Ĥ inter . Thus, Ĥ B v represents the vibrational Hamiltonian of HCl for the effective 1D potential corresponding to the interaction of flexible HCl with rigid H 2 O via a geometry that approximates that of the dimer ground state.…”

“…For the triatom–diatom complexes investigated so far, 17,25,36–38 Ĥ inter has been diagonalized in the basis of eqn (14) by using the Chebyshev version 49 of filter diagonalization. 50 The successive operation of Ĥ inter on a random initial state vector that is required by this algorithm is accomplished as follows.…”

“…Besides H 2 O/D 2 O–CO, 25 in the past couple of years the computational approach described above, that uses compact contracted bases for both intra- and intermolecular DOFs, has enabled full-dimensional (9D) and fully coupled quantum treatments of several additional noncovalently bound triatom–diatom complexes – HDO–CO, 36 H 2 O–HCl 17 and several H/D isotopologues. 37,38 These calculations have provided an unprecedented comprehensive description of their rovibrational levels tructure, intramolecular vibrational frequencies and their shifts from the isolated-monomer values, and the coupling between the inter- and intramolecular DOFs. They have also permitted unusually detailed comparison with the available microwave, FIR, and IR spectroscopic data.…”