Quasi-Classical Trajectory Calculations on a Two-State Potential Energy Surface Including Nonadiabatic Coupling Terms as Friction for D + H Collisions.

Akin to the traditional quasi-classical trajectory method for investigating the dynamics on a single adiabatic potential energy surface for an elementary chemical reaction, we carry out the dynamics on a 2-state ab initio potential energy surface including nonadiabatic coupling terms as friction terms for D + H collisions. It is shown that the resulting dynamics correctly accounts for nonreactive charge transfer, reactive non-charge transfer and reactive charge transfer processes. In addition, it leads to the formation of triatomic DH species as well.

Spectral characteristics of the flavones and anthocyanins present in passionflower (Passiflora incarnata).

Rich in antioxidants with a variety of flavones and anthocyanins, passionflower/fruit has been extensively used in food, beverage, medicinal, and natural dyes industries. The individual components present in passionflower are identified by extracting them in methanol, partitioning them between ethyl acetate and aqueous layers, and recording their ESI mass spectrometric data. The steady-state absorption and fluorescence spectra of the extract in methanol and dimethyl sulfoxide are recorded and the lifetime of the fluorescing species is reported.

The role of small molecular cations in the chemical flow of the interstellar environments.

Molecular ions have been ubiquitous in a variety of environments in the interstellar medium, from Circumstellar Envelopes to Dark Molecular Clouds and to Diffuse Clouds. Their role in the multitude of molecular processes which have been found to occur in those environments has been the subject of many studies over the years, so that we have acquired by now a complex body of data on their chemical structures, their possible function within chemical reactions and their most likely paths to formation. In the present work we review a broad range of such molecular ions, focusing exclusively on positive ions involving the smallest and simplest cations which have been either detected or conjectured as present in the interstellar medium (ISM).

Coupled three-dimensional quantum mechanical wave packet study of proton transfer in H2+ + He collisions on accurate ab initio two-state diabatic potential energy surfaces.

We have carried out fully close-coupled three dimensional quantum mechanical wave packet dynamical calculations for the reaction He+H2+→HeH++H on the ground electronic adiabatic potential energy surface and on the lowest two electronic states of newly constructed ab initio calculated diabatic potential energy surfaces for the system [Naskar et al., J. Phys.

Beyond Born-Oppenheimer Constructed Diabatic Potential Energy Surfaces for HeH.

First-principles based beyond Born-Oppenheimer theory has been employed to construct multistate global Potential-Energy Surfaces (PESs) for the HeH system by explicitly incorporating the Nonadiabatic Coupling Terms (NACTs). Adiabatic PESs and NACTs for the lowest four electronic states (1A', 2A', 3A' and 4A') are evaluated as functions of hyperangles for a grid of fixed values of the hyperradius in hyperspherical coordinates. Conical intersection between different states are validated by integrating the NACTs along appropriately chosen contours.

Improved Estimates of Host-Guest Interaction Energies for Endohedral Fullerenes Containing Rare Gas Atoms, Small Molecules, and Cations.

Endohedral fullerenes have evinced much interest from the fundamental and applications points of view. However, given the nature of the weak interaction between the guest species and the host cage in these confined systems, the interaction energy values obtained using various theoretical methods, and different basis sets vary over a wide range. For example, the reported interaction energy for the HF@C system ranges from -2.

HeH Collisions with H: Rotationally Inelastic Cross Sections and Rate Coefficients from Quantum Dynamics at Interstellar Temperatures.

We report for the first time an accurate ab initio potential energy surface for the HeH-H system in four dimensions (4D) treating both diatomic species as rigid rotors. The computed ab initio potential energy point values are fitted using an artificial neural network method and used in quantum close coupling calculations for different initial states of both rotors, in their ground electronic states, over a range of collision energies. The state-to-state cross section results are used to compute the rate coefficients over a range of temperatures relevant to interstellar conditions.

Efficiency of rovibrational cooling of HeH by collisions with He: Cross sections and rate coefficients from quantum dynamics.

By extending an earlier study [Gianturco et al., J. Chem.

Pattern formation in : An activator-inhibitor model.

Based on a careful examination of the onset of violet colored dots along the filaments in the developing floral bud stage and the formation of alternating bands of violet and white color in the matured flowers of (Passion flower), it is concluded that the pattern arises from a competition between the production of violet colored anthocyanin and the colorless flavonols along the filaments. The activator-inhibitor model of Gierer and Meinhardt along with the reaction diffusion theory of Turing is used to explain the formation of concentric rings in the flower.

Energy-transfer quantum dynamics of HeH with He atoms: Rotationally inelastic cross sections and rate coefficients.

Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH interacting with He atoms. We further use them to investigate the quantum dynamics of both the proton-exchange reaction and the purely rotational inelastic collisions over a broad range of temperatures. In current modeling studies, this cation is considered to be one of the possible cooling sources under early universe conditions after the recombination era and has recently been found to exist in the interstellar medium.

Time-dependent quantum mechanical wave packet dynamics.

Starting from a model study of the collinear (H, H) exchange reaction in 1959, the time-dependent quantum mechanical wave packet (TDQMWP) method has come a long way in dealing with systems as large as Cl + CH. The fast Fourier transform method for evaluating the second order spatial derivative of the wave function and split-operator method or Chebyshev polynomial expansion for determining the time evolution of the wave function for the system have made the approach highly accurate from a practical point of view. The TDQMWP methodology has been able to predict state-to-state differential and integral reaction cross sections accurately, in agreement with available experimental results for three dimensional (H, H) collisions, and identify reactive scattering resonances too.

Co-operativity in non-covalent interactions in ternary complexes: a comprehensive electronic structure theory based investigation.

The structure and stability of various ternary complexes in which an extended aromatic system such as coronene interacts with ions/atoms/molecules on opposite faces of the π-electron cloud were investigated using ab initio calculations. By characterizing the nature of the intermolecular interactions using an energy decomposition analysis, it was shown that there is an interplay between various types of interactions and that there are co-operativity effects, particularly when different types of interactions coexist in the same system. Graphical abstract Weak OH-π, π-π and van der Waals-π ternary systems are stabilized through dispersion interactions.

Study of Topological Effects Concerning the Lowest A″ and the Three A' States for the CO2(+) Ion.

A study of the topological effects, viz., the Jahn-Teller (JT) and Renner-Teller (RT) effects, in CO2(+) has been carried out by calculating nonadiabatic coupling terms (NACTs) at the state-averaged CASSCF level using the cc-pVTZ basis set for the lowest three A' states and one A″ state along a circular contour. Using the NACTs, the privileged adiabatic-to-diabatic transformation (ADT) angles (γ12) for 1A' and 2A' states of CO2(+) have been calculated along various circular contours.

Interpretation of the accidental predissociation of the E(1) Π state of CO.

A special case of predissociation, known as indirect or accidental predissociation observed in the Rydberg E(1)Π bound state of CO is discussed. We resort to ab initio potentials in order to determine the plausible mechanism for this predissociation. Values of the predissociation width for the valence k(3)Π state of CO, as obtained from Fermi's golden rule, are also reported.

Ab initio potential energy curves for the ground and low-lying excited states of OH and OH(-) and a study of rotational fine structure in photodetachment.

Complete basis set extrapolated ab initio potential energy curves obtained from multireference configuration interaction (MRCI) level calculations for the ground state (X(1)Σ(+)) of OH(-), and the ground state (X(2)Π) and the first excited state (A(2)Σ(+)) of OH are reported. The potential energy curves for the excited states A(1)Π, a(3)Π, and b(3)Π of OH(-) have been computed using the V6Z basis set at the MRCI level. Λ-doubling parameters p and q were calculated for the ground and the first excited vibrational states of the ground electronic state of OH using second-order perturbation theory.

Ab initio potential energy curves for the ground and low lying excited states of NH(-) and the effect of (2)Σ(±) states on Λ-doubling of the ground state X(2)Π.

Complete basis set extrapolated ab initio potential energy curves obtained from multireference configuration interaction (MRCI) level calculations for the ground state (X(2)Π) and the a(4)Σ(-) state of NH(-) and the ground state (X(3)Σ(-)) of NH are reported. The potential energy curves for the A'(2)Σ(-) and A(2)Σ(+) states of NH(-) have been computed using the V6Z basis set at the MRCI level. Λ-doubling parameters p and q are calculated for the ground and the first excited vibrational states of the ground electronic state of NH(-) using second-orderperturbation theory.

Radiative lifetimes of spin forbidden a1Δ → X3Σ- and spin allowed A3Π → X3Σ- transitions and complete basis set extrapolated ab initio potential energy curves for the ground and excited states of CH-.

The spin forbidden transition a(1)Δ → X(3)Σ(-) in CH(-) has been studied using the Breit-Pauli Hamiltonian for a large number of geometries. This transition acquires intensity through spin-orbit coupling with singlet and triplet Π states. The transition moment matrix including more than one singlet and triplet Π states was calculated at the multi-reference configuration interaction/aug-cc-pV6Z level of theory.

Collision-induced dissociation in (He, H2(+)(v = 0-2; j = 0-3)) system: a time-dependent quantum mechanical investigation.

The collision-induced process He + H(2)(+)(v = 0-2; j = 0-3) → He + H + H(+) has been investigated using a time-dependent quantum mechanical wave packet approach, within the centrifugal sudden approximation. The exchange reaction He + H(2)(+) → HeH(+) + H, which has a lower threshold, dominates over the dissociation process over the entire energy range considered in this study. The reaction cross section for both the exchange and dissociation channels and the branching ratio between the two channels have been computed on the McLaughlin-Thompson-Joseph-Sathyamurthy potential-energy surface and compared with the available experimental and quasiclassical trajectory results.

Theoretical studies of host-guest interaction in gas hydrates.

Ab initio calculations and atoms-in-molecules (AIM) analysis have been used to investigate the host-guest interaction in dodecahedral water cages using a variety of guest species that include monatomic (He, Ne, Ar, Kr, and Xe), diatomic (CO, H(2), N(2), O(2), and NO), triatomic (CO(2), NO(2), and O(3)), and polyatomic (CH(4) and NH(3)) molecules. Geometry optimization for the guest species, host cage, and their complexes was carried out using the second order Møller-Plesset perturbation method with the 6-31G** basis set. Single point energy calculations using the same method but different basis sets (6-31++G**, 6-311++G**, aug-cc-pVDZ, and aug-cc-pVTZ) were carried out for the MP2/6-31G** optimized geometries.

Stacking and spreading interaction in N-heteroaromatic systems.

π-π interactions in heteroaromatic systems are ubiquitous in biological systems. In the present study, stabilization energies of stacked and hydrogen-bonded dimers of N-heteroaromatic systems (pyridine, pyrazine, sym-triazine, and sym-tetrazine) have been computed using a benchmark quality coupled cluster through the perturbative triples (CCSD(T)) method at the estimated complete basis set (CBS) limit. In the case of stacking, monomer units are found to be stacked in parallel planes with displaced geometries.

Importance of Coriolis Coupling in Isotopic Branching in (He, HD+) collisions.

A three-dimensional time-dependent quantum mechanical wave packet approach is used to calculate the reaction probability (P(R)) and integral reaction cross section values for both channels of the reaction He + HD(+)(v = 1; j = 0) --> HeH (D)(+) + D (H) over a range of translational energy (E(trans)) on the McLaughlin-Thompson-Joseph-Sathyamurthy potential energy surface including the Coriolis coupling (CC) term in the Hamiltonian. The reaction probability plots as a function of translational energy for different J values exhibit several oscillations, which are characteristic of the system. The sigma(R) values obtained by including CC and not including it are nearly the same over the range of E(trans) investigated for the HeD(+) channel.

Structure and stability of water chains (H2O)n, n = 5-20.

The structure and stability of linear (helical) water chains (H2O)n, n = 5-20 as obtained from ab initio/DFT calculations are reported along with an atoms-in-molecules (AIM) analysis of hydrogen bond critical points and their characteristics. The resulting helical chain arrangement is one of the predominant motifs in different host environments; although they may not be the most stable, it is shown that these linear water chain clusters could exist in their own right.

The self-assembly of metaboric acid molecules into bowls, balls and sheets.

The structural motifs responsible for the formation of bowls, balls and sheets of orthoboric acid were pointed out in an earlier publication (Elango et al. J. Phys.

Structure, energetics, and reactivity of boric acid nanotubes: a molecular tailoring approach.

Cardinality guided molecular tailoring approach (CG-MTA) [Ganesh et al. J. Chem.

Hydrogen bonding in protonated water clusters: an atoms-in-molecules perspective.

This article highlights the results of a detailed study of hydrogen bonding in the first and the second solvation shells of Eigen (H3O+) and Zundel (H5O2+) cations solvated by water in a stepwise manner. It is evident from the results that an electron density analysis clearly distinguishes the first and the second solvation shell and helps in quantifying the strength of hydrogen bonding in these clusters.