Publications by authors named "John S Mancini"

Article Synopsis
  • The study focuses on diradical benzyne isomers as models to test electronic structure methods for their ability to capture static and dynamic correlation.
  • Researchers employ advanced multireference methods, such as MC-SCF and MR-AQCC, to analyze the electronic structure and singlet-triplet splittings of these isomers.
  • Findings reveal that different types of coupling (through-space vs. through-bond) significantly influence the energy gaps and geometrical properties among the benzyne isomers, aligning well with experimental data.
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This Review summarizes recent research on vibrational predissociation (VP) of hydrogen-bonded clusters. Specifically, the focus is on breaking of hydrogen bonds following excitation of an intramolecular vibration of the cluster. VP of the water dimer and trimer, HCl clusters, and mixed HCl-water clusters are the major topics, but related work on hydrogen halide dimers and trimers, ammonia clusters, and mixed dimers with polyatomic units are reviewed for completion and comparison.

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A semiglobal potential energy surface (PES) and quartic force field (QFF) based on fitting high-level electronic structure energies are presented to describe the structures and spectroscopic properties of NNHNN(+). The equilibrium structure of NNHNN(+) is linear with the proton equidistant between the two nitrogen groups and thus of D(∞h) symmetry. Vibrational second-order perturbation theory (VPT2) calculations based on the QFF fails to describe the proton "rattle" motion, i.

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Even though quartic force fields (QFFs) and highly accurate coupled cluster computations describe the OCHCO(+) cation at equilibrium as a complex between carbon monoxide and the formyl cation, two notable and typical interstellar and atmospheric molecules, the prediction from the present study is that the equilibrium C(∞v) structure is less relevant to observables than the saddle-point D(∞h) structure. This is the conclusion from diffusion Monte Carlo and vibrational self-consistent field/virtual state configuration interaction calculations utilizing a semi-global potential energy surface. These calculations demonstrate that the proton "rattle" motion (ν6) has centrosymmetric delocalization of the proton over the D(∞h) barrier lying only 393.

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We demonstrate the significant effect that large-amplitude zero-point vibrational motion can have on the high-frequency fundamental vibrations of molecular clusters, specifically small (HCl)n-(H2O)m clusters. Calculations were conducted on a many-body potential, constructed from a mix of new and previously reported semiempirical and high-level ab initio potentials. Diffusion Monte Carlo simulations were performed to determine ground-state wave functions.

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This Perspective highlights progress in ab initio quantum approaches to IR spectroscopy of water and hydrates. Here, "ab initio" refers to many-body potentials and dipole moment surfaces for flexible water and hydrates. Specifically, these are mathematical representations of two-body and three-body interactions based on permutationally invariant fitting of tens of thousands of ab initio electronic energies, a spectroscopically accurate one-body monomer potential, and four- and higher-body interactions described by the long-range interactions incorporated into, for example, the TTM3-F family of potentials.

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The centrally important role of acids in aqueous chemistry has stimulated the search for the smallest droplet of hydrochloric acid. Based on several independent quantum calculations, this appears to be the HCl(H2O)4 cluster, which dissociates into the so-called solvent ion pair (SIP), H3O(+)(H2O)3Cl(-). Experimental verification of this prediction via infra-red spectroscopy is a major challenge and despite several recent reports of this SIP, there remains uncertainty about these observations.

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Water is one of the most pervasive molecules on earth and other planetary bodies; it is the molecule that is searched for as the presumptive precursor to extraterrestrial life. It is also the paradigm substance illustrating ubiquitous hydrogen bonding (H-bonding) in the gas phase, liquids, crystals, and amorphous solids. Moreover, H-bonding with other molecules and between different molecules is of the utmost importance in chemistry and biology.

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The breaking of hydrogen bonds in molecular systems has profound effects on liquids, e.g., water, biomolecules, e.

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The hydrogen bond has been studied by chemists for nearly a century. Interest in this ubiquitous bond has led to several prototypical systems emerging to studying its behavior. Hydrogen chloride clusters stand as one such example.

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We present an on-the-fly quantum mechanical method to obtain anharmonic vibrational frequencies for molecular clusters. The basis for the method is the local-monomer model, a "divide and conquer" approach to theoretical spectroscopy, previously applied using full-dimensional surfaces [Y. Wang and J.

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We report a global, full-dimensional, ab initio potential energy surface describing the HCl-H2O dimer. The potential is constructed from a permutationally invariant fit, using Morse-like variables, to over 44,000 CCSD(T)-F12b∕aug-cc-pVTZ energies. The surface describes the complex and dissociated monomers with a total RMS fitting error of 24 cm(-1).

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(rac)-1,1'-Binaphthyl-based simple receptors 1 and 2 have been designed, synthesized and studied theoretically. The receptors utilize naphthyridine as the binding motifs for complexation of dicarboxylic acids in CHCl(3). The emission of the BINOL moiety was monitored experimentally to ascertain the selectivity and sensitivity of the receptors.

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