Theoretical Spectroscopic Study of Two Ketones of Atmospheric Interest: Methyl Glyoxal (CHCOCHO) and Methyl Vinyl Ketone (CHCOCH═CH).

Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core-valence correlation-consistent basis sets. The work focuses on the far-infrared region. At the employed level of theory, the rotational constants can be determined to within a few megahertz of the experimental data.

Neutral and Multicharged Ions of Small Aluminum Oxides: Structures, Spectroscopy, and Energetics.

We use accurate methodologies at the Coupled Cluster level to compute the stable forms of AlO ( = 1, 2; = 1, 2; = 0-3) species for which we derive an accurate set of geometrical and vibrational spectroscopic data. We also determine their adiabatic single, double, and triple ionization energies. These spectroscopic and thermodynamical data may help for identifying these species in laboratory, in astrophysical media, and in plasma and confirm previous observations of multi-charged AlO clusters by Atom Probe Tomography (ATP) coupled to mass spectrometry.

Explicitly correlated potential energy surface of the CO-CO van der Waals dimer and applications.

The four-dimensional-potential energy surface (4D-PES) of the CO2-CO van der Waals complex is generated using the explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in conjunction with the augmented correlation-consistent triple zeta (aug-cc-pVTZ) basis set. This 4D-PES is developed over the set of inter-molecular coordinates and where the CO2 and CO monomers are treated as rigid rotors. Afterwards, analytic fits of this 4D-PES are carried out.

Effects of complexation with sulfuric acid on the photodissociation of protonated Cinchona alkaloids in the gas phase.

The effect of complexation with sulfuric acid on the photo-dissociation of protonated Cinchona alkaloids, namely cinchonidine (Cd), quinine (Qn) and quinidine (Qd), is studied by combining laser spectroscopy with quantum chemical calculations. The protonated complexes are structurally characterized in a room-temperature ion trap by means of infra-red multiple photon dissociation (IRMPD) spectroscopy in the fingerprint and the ν(XH) (X = C, N, O) stretch regions. Comparison with density functional theory calculations including dispersion (DFT-D) unambiguously shows that the complex consists of a doubly protonated Cinchona alkaloid strongly bound to a bisulfate HSO4- anion, which bridges the two protonated sites of the Cinchona alkaloid.

Inelastic scattering dynamics of ortho and para hydronium ions, o-HO and p-HO, with He at low temperature.

The hydronium ion, H3O+, presents a crucial key to understanding the chemistry of the interstellar clouds where it has been frequently observed. The present paper is devoted to studying the inelastic scattering of both forms of the hydronium ion, o-H3O+ and p-H3O+, by helium atoms. The interaction potential between H3O+ and He was mapped in Jacobi coordinates leading to a new three dimensional potential energy surface (3D-PES) at the CCSD(T)/aug-cc-pVQZ+BF (CCSD(T)/AVQZ+BF) level of theory.

Stereochemistry-dependent hydrogen bonds stabilise stacked conformations in jet-cooled cyclic dipeptides: (LD) vs. (LL) cyclo tyrosine-tyrosine.

Tyrosine-containing cyclic dipeptides based on a diketopiperazine (DKP) ring are studied under jet-cooled conditions using resonance-enhanced multi-photon ionisation (REMPI), conformer-selective IR-UV double resonance vibrational spectroscopy and quantum chemical calculations. The conformational landscape of the dipeptide containing natural L tyrosine (Tyr), namely c-LTyr-LTyr strongly differs from that of its diastereomer c-LTyr-DTyr. A similar family of conformers exists in both systems, with one aromatic ring folded on the dipeptide DKP ring and the other one extended.

Accurate theoretical characterization of dioxygen difluoride: a problem resolved.

Dioxygen difluoride is a tough molecule that has defied accurate theoretical description for many decades. In the present work we have identified the reason for this resistance: the flatness of the OO, and more important OF, stretching potential energy curves, which make it difficult to localise the global minimum. It is not related to the weak multi-reference character.

Mobility gap and quantum transport in a functionalized graphene bilayer.

In a Bernal graphene bilayer, carbon atoms belong to two inequivalent sublattices A and B, with atoms that are coupled to the other layer by [Formula: see text] bonds belonging to sublattice A and the other atoms belonging to sublattice B. We analyze the density of states and the conductivity of Bernal graphene bilayers when atoms of sublattice A or B only are randomly functionalized. We find that for a selective functionalization on sublattice B only, a mobility gap of the order of 0.

Does the Residues Chirality Modify the Conformation of a Cyclo-Dipeptide? Vibrational Spectroscopy of Protonated Cyclo-diphenylalanine in the Gas Phase.

The structure of a protonated diketopiperazine dipeptide, cyclo-diphenylalanine, is studied by means of infrared multiple photon dissociation spectroscopy combined with quantum chemical calculations. Protonation exclusively occurs on the oxygen site and, in the most stable conformer, results to an intramolecular OH···π interaction, accompanied by a CH···π interaction. Higher-energy conformers with free OH and NH···π interactions are observed as well, due to kinetic trapping.

The gas-phase structure of dimethyl peroxide.

There has been a disagreement amongst experimentalists and between experimentalists and theoreticians as to the gas-phase structure of dimethyl peroxide. We have investigated this problem with high-level CCSD(T)-F12 and MRCI procedures. There can be no doubt anymore that, at the minimum of the potential energy surface, the COOC fragment has a trans-structure.

Solvation energies of the proton in ammonia explicitly versus temperature.

We provide in this work, the absolute solvation enthalpies and the absolute solvation free energies of the proton in ammonia explicitly versus temperature. As a result, the absolute solvation free energy of the proton remains quite constant for temperatures below 200 K. Above this temperature, it increases as a linear function of the temperature: ΔG(H,T)=-1265.

Structures and spectroscopy of medium size protonated ammonia clusters at different temperatures, H(NH).

Structures of protonated ammonia clusters (H(NH)) are very important for the determination of pKa's and solvation energies of the proton in ammonia. In this work, their structures were investigated at M06-2X/6-31++g(d,p) level of theory, for n=10-16 and for temperatures ranging from 0 to 400 K. In the cluster community, this is the first theoretical study on the protonated ammonia clusters larger than the nonamer.

Structures and spectroscopy of protonated ammonia clusters at different temperatures.

The accurate determination of the solvation energies of a proton in ammonia is based on the precise knowledge of the structures of neutral and protonated ammonia clusters. In this work, we have investigated all the possible and stable structures of protonated ammonia clusters H(NH), along with their isomeric distribution at a specific temperature. New significant isomers are reported here for the first time and show that the structures of protonated ammonia clusters are not only branched linear as assumed by all previous authors.

Toward the laboratory identification of [O,N,S,S] isomers: Implications for biological NO chemistry.

Benchmark ab initio calculations are performed to investigate the stable isomers of [O,N,S,S]. These computations are carried out using coupled cluster (RCCSD(T)) and explicitly correlated coupled cluster methods (RCCSD(T)-F12). In addition to the already known cis isomer of SSNO, nine other stable forms are predicted.

Structures and relative stabilities of ammonia clusters at different temperatures: DFT vs. ab initio.

A hydrogen bond network in ammonia clusters plays a key role in understanding the properties of species embedded in ammonia. This network is dictated by the structures of neutral ammonia clusters. In this work, structures of neutral ammonia clusters (NH3)n(=2-10) have been studied at M06-2X/6-31++G(d,p) and MP2/6-31++g(d,p) levels of theory.

On the role of HNS and HSN as light-sensitive NO-donors for delivery in biological media.

Results are presented that suggest that thiazyl hydride (HSN)/thionitrosyl hydride (sulfimide, HNS) can be used as light-sensitive compounds for NO-delivery in biological media, as well as markers for the possible detection of intermediates in nitrites + H2S reactions at the cellular level. They are expected to be more efficient than the HNO/HON isovalent species and hence they should be considered instead. A set of characteristic spectroscopic features are identified that could aid in the possible detection of these species in the gas phase or in biological environments.

Potential energy surface of the CO2-N2 van der Waals complex.

Four-dimensional potential energy surface (4D-PES) of the atmospherically relevant CO2-N2 van der Waals complex is generated using the explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in conjunction with the augmented correlation consistent triple zeta (aug-cc-pVTZ) basis set. This 4D-PES is mapped along the intermonomer coordinates. An analytic fit of this 4D-PES is performed.

Explicit correlation treatment of the potential energy surface of CO2 dimer.

We present an extensive study of the four-dimensional potential energy surface (4D-PES) of the carbon dioxide dimer, (CO2)2. This PES is developed over the set of intermolecular coordinates. The electronic computations are carried out at the explicitly correlated coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)-F12] level of theory in connection with the augmented correlation-consistent aug-cc-pVTZ basis set.

Rotationally inelastic dynamics of LiH (X(1)Σ(+), v = 0) in collisions with Ar: State-to-state inelastic rotational rate coefficients.

A theoretical study of rotational collision of LiH(X(1)Σ(+),v = 0, J) with Ar has been carried out. The ab initio potential energy surface (PES) describing the interaction between the Ar atom and the rotating LiH molecule has been calculated very accurately and already discussed in our previous work [Computational and Theoretical Chemistry 993 (2012) 20-25]. This PES is employed to evaluate the de-excitation cross sections.

Structures of protonated methanol clusters and temperature effects.

The accurate evaluation of pKa's, or solvation energies of the proton in methanol at a given temperature is subject to the determination of the most favored structures of various isomers of protonated (H(+)(MeOH)n) and neutral ((MeOH)n) methanol clusters in the gas phase and in methanol at that temperature. Solvation energies of the proton in a given medium, at a given temperature may help in the determination of proton affinities and proton dissociation energies related to the deprotonation process in that medium and at that temperature. pKa's are related to numerous properties of drugs.

On the accuracy of explicitly correlated methods to generate potential energy surfaces for scattering calculations and clustering: application to the HCl-He complex.

We closely compare the accuracy of multidimensional potential energy surfaces (PESs) generated by the recently developed explicitly correlated coupled cluster (CCSD(T)-F12) methods in connection with the cc-pVXZ-F12 (X = D, T) and aug-cc-pVTZ basis sets and those deduced using the well-established orbital-based coupled cluster techniques employing correlation consistent atomic basis sets (aug-cc-pVXZ, X = T, Q, 5) and extrapolated to the complete basis set (CBS) limit. This work is performed on the benchmark rare gas-hydrogen halide interaction (HCl-He) system. These PESs are then incorporated into quantum close-coupling scattering dynamical calculations in order to check the impact of the accuracy of the PES on the scattering calculations.

Solvation Energies of the Proton in Methanol.

pKa's, proton affinities, and proton dissociation free energies characterize numerous properties of drugs and the antioxidant activity of some chemical compounds. Even with a higher computational level of theory, the uncertainty in the proton solvation free energy limits the accuracy of these parameters. We investigated the thermochemistry of the solvation of the proton in methanol within the cluster-continuum model.