[AnX(3)](2)(μ-η(2):η(2)-N(2)) (An = Th-Pu; X = F, Cl, Br, Me, H, OPh) have been studied using relativistic density functional theory. Geometric and vibrational data suggest that metal→N(2) charge transfer maximises at the protactinium systems, which feature the longest N-N bonds and the smallest σ(N-N), as a result of partial population of the N-N π* orbitals. There is very strong correlation of the standard quantum theory of atoms-in-molecules (QTAIM) metrics - bond critical point ρ, ∇(2)ρ and H and delocalisation indices - with An-N and N-N bond lengths and σ(N-N), but the correlation with An-N interaction energies is very poor. A similar situation exists for the other systems studied; neutral and cationic actinide monoxide and dioxides, and AnL(3+) and AnL(3)(3+) (L = pyridine (Py), pyrazine (Pz) and triazine (Tz)) with the exception of some of the ∇(2)ρ data, for which moderate to good correlations with energy data are sometimes seen. By contrast, in almost all cases there is very strong correlation of interaction and bond energies with |ΔQ(QTAIM)(An)|, a simple QTAIM metric which measures the amount of charge transferred to or from the actinide on compound formation.

The spectral features of H3O+ between 3000 and 3800 cm-1 are known to be dominated by coupling between the fundamentals of stretching modes and the overtones of bending modes. A strong Fermi resonance (FR) pattern has been observed in Ar-tagged H3O+, and the sensitive dependence of the FR pattern on the number of Ar tags has been analyzed by Li et al. [J. Phys. Chem. A, 2015, 119(44), 10887]. Based on ab initio anharmonic calculations with MP2/aug-cc-pvDZ, Tan et al. investigated the influence of different types of rare gas and found a counter-intuitive trend that the strength of the coupling between the overtones of bending modes and the fundamentals of stretching modes decreases as the strength of solvation increases [Phys. Chem. Chem. Phys., 2016, 18(44), 30721]. In the present work, we combine both experimental and theoretical tools to gain a better understanding of the FR in H3O+. Experimentally, spectra of H3O+ with light and much more weakly-bound Ne tags were measured for the first time and spectra of Ar-tagged H3O+ were re-measured for comparison. Theoretically, we have implemented several computational schemes to improve both the accuracy and efficiency of the anharmonic treatments with higher-level ab initio methods (up to CCSD/aug-cc-pVTZ). With the good agreement between the experimental and theoretical spectra, we are confident about the prediction of the modulation of coupling strength by the solvation environments.

Complex vibrational features of solvated hydronium ion, H 3 O + , in 3 μm enable us to look into the vibrational coupling among O−H stretching modes and other degrees of freedom. Two anharmonic coupling schemes have often been engaged to explain observed spectra: coupling with the OH bending overtone, known as Fermi resonance (FR), has been proposed to account for the splitting of the OH stretch band at ∼3300 cm −1 in H 3 O + •••Ar 3 , but an additional peak in H 3 O + ••• (N 2 ) 3 at the similar frequency region has been assigned to a combination band (CB) with the lowfrequency intermolecular stretches. While even stronger vibrational coupling is expected in H 3 O + ••• (H 2 O) 3 , such pronounced peaks are absent. In the present study, vibrational spectra of H 3 O + •••Kr 3 and H 3 O + •••(CO) 3 are measured to complement the existing spectra. Using ab initio anharmonic algorithms, we are able to assign the observed complex spectral features, to resolve seemingly contradictory notions in the interpretations, and to reveal simple pictures of the interplay between FR and CB.

Elucidating the dynamic couplings of hydrogen bonds remains an important and challenging goal for spectroscopic studies of bulk systems, because their vibrational signatures are masked by the collective effects of the fluctuation of many hydrogen bonds. Here we utilize sizeselected infrared spectroscopy based on a tunable vacuum ultraviolet free electron laser to unmask the vibrational signatures for the dynamic couplings in neutral trimethylamine−water and trimethylamine−methanol complexes, as microscopic models with only one single hydrogen bond holding two molecules. Surprisingly broad progression of OH stretching peaks with distinct intensity modulation over ∼700 cm −1 is observed for trimethylamine−water, while the dramatic reduction of this progression in the trimethylamine−methanol spectrum offers direct experimental evidence for the dynamic couplings. State-of-the-art quantum mechanical calculations reveal that such dynamic couplings are originated from strong Fermi resonance between the stretches of hydrogen-bonded OH and several motions of the solvent water/ methanol, such as translation, rocking, and bending, which are significant in various solvated complexes commonly found in atmospheric and biological systems.

Infrared spectra for as eries of asymmetric protonbound dimers with protonated trimethylamine (TMA-H +)a s the proton donor were recorded and analyzed.T he frequency of the N-H + stretching mode is expected to red shift as the proton affinity of proton acceptors increases.T he observed band, however,s hows ap eculiar splitting of approximately 300 cm À1 with the intensity shifting pattern resembling at wolevel system. Theoretical investigation reveals that the observed band splitting and its extraordinarily large gap of around 300 cm À1 is aresult of strong coupling between the fundamental of the proton stretching mode and overtone states of the two proton bending modes,t hat is commonly knowna sF ermi resonance (FR). We also provide ageneral theoretical model to link the strong FR coupling to the quasi-two-level system. Since the model does not depend on the molecular specification of TMA-H + ,t he strong coupling we observed is an intrinsic property associated with proton motions.

An ideal electrical wire needs not only good conductivity for its central conductor but also a surrounding insulating layer to protect its current from leaking. We show that the extended metal-atom chain is a promising candidate to be the smallest molecular electrical wire for future practical applications. The electron can move through core metals, while the internal current is insulated from outside by the surrounding π-conjugated functional group. Moreover, we also show the existence of unavoidable hidden pathways at each site to the electrodes in a nanoscaled quantum circuit. Nevertheless, the Kirchhoff's junction rule still holds when the current inflow and outflow arising from the additional terms of the self-energies of contacts are included.It is an important issue to find potential single molecular wires that can be functional units of nanotransistors for electronic apparatus application. 1 The current understanding of the electron transfer through a single molecular wire is mainly built on organic molecules with and without π-electron conjugated systems. [2][3][4] People have realized that in order to reach high conductivity the delocalized electrons in the bridge are needed to play the role of charge transfer. Pure organic molecules such as oligo(phenylene ethynylene) (OPE) 5 and oligo(phenylene vinylene) (OPV) 6 are often discussed for their long π-conjugated chains. However, in the fabrication of nanodevices, it is unavoidable to have multiple molecular wires packed in proximity. The wave function of one conductor can mix with the other through the overlap of electron clouds, which may result in the unwanted transversal hopping of charge carriers. In view of this, one-dimensional metal string complexes 7 can be a promising candidate without the above problem.Extended metal-atom chain (EMAC) complexes consist of a central metal-containing backbone and four specifically designed polydentate ligands. The use of the poly(pyridylamine) ligand with a flexible 1D metal chain developed individually by Cotton and Peng has led to the isolation of metal chains with 3-9 metal atoms. 7 Structurally, the EMAC is possibly the smallest version of an ordinary electrical wire that one can synthesize. In this article, we focus on the conductive properties of the trinuclear compound of the type, [M 3 (µ 3 -dpa) 4 (NCS) 2 ] (M ) Cr, Co, Ni; dpa ) syn-syn-bis(R-pyridyl)amido) (see Figure 1). Experimentally, these mixed-valence stacks of organic as well as inorganic molecules exhibit unusual electrical properties. 8-10 Bond orders for the symmetric and neutral complexes of nickel, cobalt, and chromium are 0, 0.5, and 1.5, which indicate the degree of the electron delocalization and thus the efficiency of the electron transfer through metal centers. 8,11 To calculate the electron-transfer properties, we use the code Hückel IV 3.0, 12 which is based on the nonequilibrium Green's function (NEGF) formalism. The influence of the outside effect (contact) is incorporated into the main body of the device through self-energy matric...

Methylamine (MMA) is one of the simplest amines, and the vibrational spectra of its dimer have recently been obtained experimentally. The vibrational spectra of NH stretch modes were well resolved, but the complex features of the CH group could not be fully accounted for even with the assistance of ab initio molecular dynamics (AIMD) with various density functional methods. In this study, we carried out anharmonic vibrational calculations on MMA clusters up to tetramers using MP2/aug-cc-pVDZ to examine vibrational coupling among CH/NH and compute the vibrational spectra of these clusters between 2800 and 3500 cm. We found that the main origin of the complexity between 2800 and 3000 cm was caused by Fermi resonance (FR) between the stretching and bending overtones of the CH group. This spectral feature becomes simpler in trimers and tetramers. Furthermore, Fermi resonance in the NH group is found to be very strong. In the MMA dimer, no noticeable FR features can be found; however, in its trimers and tetramers, the enhancement of hydrogen bond strength due to the cooperative effect will cause the N-H stretching mode to red-shift to revert the energy order of the fundamental of the N-H stretch and overtone of N-H bending between n = 3 and n = 4. Therefore, significant re-distribution of the intensities of the bands at 3200 and 3300 cm should be seen.

Strong coupling between stretching fundamentals and bending overtones of vibrational modes, known as Fermi resonance (FR), has been observed for proton motions in the protonated trimethylamine–water cluster. To investigate the...