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Spectroscopic exploration of sulfur-centered hydrogen bonding involving a thiol group (S–H) as the hydrogen bond donor is scarce in the literature. Herein, we have investigated 1:1 complexes of 2-fluorothiophenol (2-FTP) with methanol (MeOH) and ethanol (EtOH) in the gas phase to examine the physical characteristics and strength of the S–H⋯O hydrogen bond. Structures, conformations, and the strength of the S–H⋯O interaction are investigated by measuring the electronic and Infrared (IR) spectra of the two complexes employing resonant two-photon ionization, UV–UV hole-burning, and IR–UV double resonance spectroscopic techniques combined with quantum chemical calculations. Three conformers of 2-FTP⋯MeOH and two conformers of 2-FTP⋯EtOH have been detected in the experiment. A comparison of the IR spectra obtained from the experiment with those of the low-energy conformers of 2-FTP⋯MeOH and 2-FTP⋯EtOH predicted from the theory confirms that all the observed conformers of the two complexes are primarily S–H⋯O hydrogen bonded. The IR red-shifts found in the S–H stretching frequencies in 2-FTP⋯MeOH and 2-FTP⋯EtOH concerning that in 2-FTP are ∼76 and ∼88 cm−1, respectively, which are much larger than that was reported earlier in the 2-FTP⋯H2O complex (30 cm−1). The strength and physical nature of different noncovalent interactions, including the S–H⋯O hydrogen bond existing in the complexes, are further analyzed using natural bond orbital analysis, quantum theory of atoms in molecules, and localized molecular orbital-energy decomposition analysis. The current investigation reveals that the S–H⋯O hydrogen bond can be strengthened by judicial choices of the hydrogen bond acceptors of higher proton affinities. [ABSTRACT FROM AUTHOR]

Vibrational spectra in the acetylenic and aromatic C–H stretching regions of phenylacetylene and fluorophenylacetylenes, viz., 2-fluorophenylacetylene, 3-fluorophenylacetylene, and 4-fluorophenylacetylene, were measured using the IR-UV double resonance spectroscopic method. The spectra, in both acetylenic and aromatic C–H stretching regions, were complex exhibiting multiple bands. Ab-initio anharmonic calculations with quartic potential using B97D3/6-311++G(d,p) and vibrational configuration interaction were able to capture all important spectral features in both the regions of the experimentally observed spectra for all four molecules considered in the present work. Interestingly, for phenylacetylene, the spectrum in the acetylenic C–H stretching region emerges due to anharmonic coupling of modes localized on the acetylenic moiety along with the other ring modes, which also involve displacements on the acetylenic group, which is in contrast to what has been proposed and propagated in the literature. In general, this coupling scheme is invariant to the fluorine atom substitution. For the aromatic C–H stretching region, the observed spectrum emerges due to the coupling of the C–H stretching with C–C stretching and C–H in-plane bending modes. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) spectra of H3O+⋯Xn (X = Ar, N2, and CO, n = 1–3) in the first overtone region of OH-stretching vibrations (4800–7000 cm−1) were measured. Not only OH-stretching overtones but also several combination bands are major features in this region, and assignments of these observed bands are not obvious at a glance. High-precision anharmonic vibrational simulations based on the discrete variable representation approach were performed. The simulated spectra show good agreement with the observed ones and provide firm assignments of the observed bands, except in the case of X = CO, in which higher order vibrational mode couplings seem significant. This agreement demonstrates that the present system can be a benchmark for high precision anharmonic vibrational computations of NIR spectra. Band broadening in the observed spectra becomes remarkable with an increase of the interaction with the solvent molecule (X). The origin of the band broadening is explored by rare gas tagging experiments and anharmonic vibrational simulations of hot bands. [ABSTRACT FROM AUTHOR]

Previous exploration of the conformational space of sodiated mono-saccharides using a random search algorithm leads to ∼103 structurally distinct conformers covering an energy range of ∼150 kJ mol−1. Thus, it is reasonable to expect that the number of distinct conformers for a given disaccharide would be on the order of 106. Efficient identification of distinct conformers at the first-principles level has been demonstrated with the assistance of neural network potential (NNP) with an accuracy of ∼1 kJ mol−1 compared to DFT. Leveraging a local minima database of neutral and sodiated glucose (Glc), we develop algorithms to systematically explore the conformation landscape of 19 Glc-based sodiated disaccharides. To accelerate the exploration, the NNP method is implemented. The NNP achieves an accuracy of ∼2.3 kJ mol−1 compared to DFT, offering a comparable quality to that of DFT. Through a multi-model approach integrating DFTB3, NNP and DFT, we can rapidly locate low-energy disaccharide conformers at the first-principles level. The methodology we show here can be used to efficiently explore the potential energy landscape of any di-saccharides when first-principles accuracy is required. [ABSTRACT FROM AUTHOR]

The structures of the formyl ion (HCO+) and its rare gas tagged counterparts (Rg–HCO+, Rg = He, Ne, Ar, Kr, and Xe) were studied at the coupled-cluster singles, doubles, and perturbative triples [CCSD(T)]/aug-cc-pVTZ level of theory and basis set. A linear structure for these tagged complexes was predicted. The Rg binding energies for Rg–HCO+ are also examined at the CCSD(T) level. It was found that the binding interaction increases from He–HCO+ to Xe–HCO+. A multilevel potential energy surface built at the CCSD(T) and second-order Møller–Plesset perturbation levels of theory were used to study these species' vibrational spectra. By changing the Rg in the first-solvation shell for HCO+, the Fermi resonance interaction between the first H+ bend overtone and the asymmetric and symmetric H–C–O stretches can be modulated. This Fermi resonance modulation is demonstrated by examining a series of rare gas solvated HCO+. [ABSTRACT FROM AUTHOR]

Matrix isolation experiments have been successfully employed to extensively study the infrared spectrum of several proton-bound rare gas complexes. Most of these studies have focused on the spectral signature for the H+ stretch (ν3) and its combination bands with the intermolecular stretch coordinate (ν1). However, little attention has been paid to the Fermi resonance interaction between the H+ stretch (ν3) and H+ bend overtone (2ν2) in the asymmetric proton-bound rare gas dimers, RgH+Rg′. In this work, we have investigated this interaction on KrH+Rg and XeH+Rg with Rg = (Ne, Ar, Kr, and Xe). A multilevel potential energy surface (PES) was used to simulate the vibrational structure of these complexes. This PES is a dual-level comprising of second-order Møller–Plesset perturbation theory and coupled-cluster singles doubles with perturbative triples [CCSD(T)] levels of ab initio theories. We found that when both the combination bands (nν1 + ν3) and bend overtone 2ν2 compete to borrow intensity from the ν3 band, the latter wins over the former, which then results in the suppression of the nν1 + ν3 bands. The current simulations offer new assignments for the ArH+Xe and KrH+Xe spectra. Complete basis set (CBS) binding energies for these complexes were also calculated at the CCSD(T)/CBS level. [ABSTRACT FROM AUTHOR]

The appearance of multiple bands in the N–H stretching region of the infrared spectra of the neutral methylamine dimer and trimer is a sign of NH bend–stretch anharmonic coupling. Ab initio anharmonic calculations were carried out in a step-wise manner to reveal the origin of various bands observed in the spectrum of the methylamine dimer. A seven-dimensional potential energy surface involving symmetric and asymmetric stretching and bending vibrations of both the hydrogen bond donor and the acceptor along intermolecular-translational modes was constructed using the discrete variable representation approach. The resulting spectrum of the dimer shows five bands that can be attributed to the symmetric stretching ( ν sym D ), asymmetric stretchin ( ν asym D ), and bending overtone (2 ν bend D ) of the donor moiety. These appear along with the combination band arising out of bending vibrations of the donor and acceptor ( ν bend D + ν bend A ) and with the combination of the intermolecular translational mode over the donor bending overtone ( ν trans + 2 ν bend D ). The spectrum of the trimer essentially consists of all the features seen in the dimer with marginal changes in band positions. The analysis of the experimental spectra based on the two-state deperturbation model and ab initio anharmonic calculations yield a matrix element of about 40 cm−1 for the N–H bend–stretch Fermi resonance coupling. In general, the IR spectra of the hydrogen-bonded amino group depict three sets of bands that arise due to bend–stretch Fermi resonance coupling. [ABSTRACT FROM AUTHOR]

We use periodic DFT calculations at LDA and PBE level to investigate 3d transition metal dihalide (TMDH) monolayers in H‐ and T‐phase. By analyzing the phonon dispersion, we have obtained a rough overview which combinations may form stable structures. We have focused on identifying and explaining trends in the predicted electronic properties. Although their geometric structures are simple, the associated electronic and magnetic properties are not as easy to understand. At first glance, it seems that there is no clear trend, as even isovalence‐electronic TMDH monolayers formed from the same metal but different halides can feature different magnetic moments. The identification of potential trends is further complicated by the fact that for a significant number of species, LDA results and PBE results predict different ground‐state electronic structures. By rigorously analyzing the potential energy surfaces associated with different magnetic moments, we could show that the apparent inconsistencies can be easily understood as a result of the differences in the relative energy between electronic states of different magnetic moments. We further show that the trends in the band gaps can be easily rationalized by an electron counting rule based on simple symmetry arguments. [ABSTRACT FROM AUTHOR]

The infrared spectrum of proton-bound rare gas dimers has been extensively studied via matrix isolation spectroscopy. However, little attention has been paid on their spectrum in the gas phase. Most of the Rg2H+ has not been detected outside the matrix environment. Recently, ArnH+ (n = 3-7) has been first detected in the gas-phase [D. C. McDonald et al., J. Chem. Phys. 145, 231101 (2016)]. In that work, anharmonic theory can reproduce the observed vibrational structure. In this paper, we extend the existing theory to examine the vibrational signatures of Rg2H+, Rg = {Ne, Ar, Kr, and Xe}. The successive binding of Rg to H+ was investigated through the calculation of stepwise formation energies. It was found that this binding is anti-cooperative. High-level full-dimensional potential energy surfaces at the CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVQZ were constructed and used in the anharmonic calculation via discrete variable representation. We found that the potential coupling between the symmetric and asymmetric Rg-H+ stretch (ν1 and ν3 respectively) causes a series of bright n1ν1 + ν3 progressions. From Ne2H+ to Xe2H+, an enhancement of intensities for these bands was observed. [ABSTRACT FROM AUTHOR]

Infrared-vacuum ultraviolet (IR-VUV) spectra of neutral dimethylamine clusters, (DMA)n (n = 2–5), were measured in the spectral range of 2600–3700 cm−1. The experimental IR-VUV spectra show NH stretch modes gradually redshift to 3200-3250 cm−1 with the increase in the cluster size and complex Fermi Resonance (FR) pattern of the CH3 group in the 2800–3000 cm−1 region. Ab initio anharmonic vibrational calculations were performed on low-energy conformers of (DMA)2 and (DMA)3 to examine vibrational coupling among CH/NH and to understand the Fermi resonance pattern in the observed spectra features. We found that the redshift of NH stretching mode with the size of DMA cluster is moderate, and the overtone of NH bending modes is expected to overlap in frequency with the CH stretching fundamental modes. The FR in CH3 groups is originated from the strong coupling between CH stretching fundamental and bending overtone within a CH3 group. Well-resolved experimental spectra also enable us to compare the performance of ab initio anharmonic algorithms at different levels. [ABSTRACT FROM AUTHOR]