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The anion C5N− is one of the largest linear (C,N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1–300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions.

We report for the first time an accurate ab initio potential energy surface for the HeH+-H2system 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. By comparing the four dimensional quantum results with those obtained by a reduced-dimensions approach that treats the H2molecule as an averaged, nonrotating target, it is shown that the reduced dimensionality results are in good accord with the four dimensional results as long as the HeH+molecule is not initially rotationally excited. By further comparing the present rate coefficients with those for HeH+-H and for HeH+-He, we demonstrate that H2molecules are the most effective collision partners in inducing rotational excitation in HeH+cation at interstellar temperatures. The rotationally inelastic rates involving o-H2and p-H2excitations are also obtained and they turn out to be, as in previous systems, orders of magnitude smaller than those involving the cation. The results for the H2molecular partner clearly indicate its large energy-transfer efficiency to the HeH+system, thereby confirming its expected importance within the kinetics networks involving HeH+in interstellar environments., Austrian Science Fund (FWF); Spanish Government (MINECO); Ministerio de Ciencia e Innovación (MCIN) / Agencia Estatal de Investigació (AEI) 10.13039/501100011033

Chemistry is a broad discipline that overlaps extensively with Biology, Medicine, Materials science, Physics, and many other areas. There has often been a view expressed and shared among Indian chemists that the discipline has not been properly represented, and its vitality and vigor were not adequately recognized in India.

We report for the first time an accurate ab initio potential energy surface for the HeH

By extending an earlier study [Gianturco et al., J. Chem. Phys. 154, 054311 (2021)] on the purely rotational excitation of HeH

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 Passiflora incarnata (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.

Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH

Dynamics of (He, H2+) Collisions

Atomic and Molecular Clusters: Designer Materials for the Nanoworld

A time-dependent quantum mechanical approach has been used to investigate the reaction He+HD+(v = 0 - 4,j = 0 - 3)→HeH++D; HeD+ + H in three dimensions for total angular momentum J = 0. The vib-rotation (v,j) state-selected reaction probability (PRv,j) is shown to increase with v over the collision energy (Etrans) range (0.95-2.25 eV) investigated for both the exchange channels, in accord with the experimental results. The isotopic branching ratio F = PR(HeH+)/PR(HeD+) generally remains less than unity for different v states at different Etrans in agreement with experiment. But at Etrans= 1.0 eV, for v = 4, F obtained from our calculations for j = 0 of HD+ is ∼0.8, in excellent agreement with the earlier quasiclassical trajectory calculations, but a factor of 2 less than that obtained from experiment. This difference could arise from the inclusion of nonzero j states in the experimental study, as PRv,j is found to be j dependent for both the channels. While PRv,j (HeH+) decreases initially with increase in j from 0 to 2 and then increases when j is increased further to 3, PRv,j (HeD+) reveals an unusual j dependence; it is larger for even j states of HD+ than for odd j. As a result, F is strongly dependent on j, in contrast to the marginal dependence shown by the earlier quasiclassical trajectory calculations. © 1999 American Institute of Physics.

This paper presents a comprehensive study on the effect of citric acid, sodium benzoate, sodium salicylate, and urea (hydrotropes) on the solubility and mass-transfer coefficient for the extraction of butyl acetate in water. The influence of a wide range of hydrotrope concentrations (0-3.0 mol/L) and different temperatures (303 K to 333 K) on the solubility of butyl acetate has been studied. The influence of different hydrotrope concentrations on the mass-transfer coefficient for the butyl acetate +water system has been ascertained. The Setschenow constant, K s , a measure of the effectiveness of hydrotrope, has been determined for each case. The solubility of butyl acetate increases with increase in hydrotrope concentration and also with temperature. Consequent to the increase in the solubility of butyl acetate, the mass-transfer coefficient was also found to increase with increase in hydrotrope concentration. A minimum hydrotrope concentration was found essential to show a significant increase in the solubility and mass-transfer coefficient for the butyl acetate + water system. The enhancement factor, which is the ratio of the value in the presence and absence of a hydrotrope, is reported for both solubility and mass-transfer coefficient.

The influence of a femtosecond laser pulse on an adsorbate molecule−metal surface system is investigated by considering a time-dependent coupling between the ground- and excited-state potential energy curves using the time-dependent quantum mechanical wave packet approach. It is shown that the probability of desorption is strongly dependent on the duration of the coupling and the image−charge attraction and that it increases with increase in vibrational excitation of the metal−adsorbate bond.

Vib-rotational state-selected and energy resolved total reaction probabilities for the title reaction in three dimensions are calculated on the McLaughlin–Thompson–Joseph–Sathyamurthy potential energy surface, by the time-dependent wave packet (WP) method for the total angular momentum J=0. The probabilities as obtained by the time-energy mapping of the reactive flux of the WP across a dividing surface in the asymptotic product channel reveal a large number of narrow resonances, in agreement with the time-independent quantum mechanical results available in the literature. While initial vibrational excitation of H2+ is shown, in general, to enhance the reaction probability considerably, in agreement with the experimental observations, rotational excitation has only a marginal influence.

We examine the possibility of existence of dynamical resonances in collinear (He,HD+) and (He,DH+) collisions by analyzing their respective transition state spectra on the McLaughlin‐Thompson‐Joseph‐Sathyamurthy potential energy surface (PES). The spectra are computed by Fourier transforming the temporal autocorrelation function, C(t), of the initial wave packet. Some of the well resolved resonances are analyzed by computing their eigenfunctions and lifetimes. The vibrational state (v) ‐ selected energy resolved reaction probabilities (PRv(E)) for collinear (He,HD+) and (He,DH+) collisions are also calculated on the same PES by computing the reactive flux in the product channel. The PRv(E) values for HeHD+ show a characteristic staircase‐like structure that can be related to threshold resonances. The PRv(E) values for HeDH+ on the other hand, are highly oscillatory, in keeping with the densely packed transition state spectrum.

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. The computed radiative lifetime of 5.63 s is in good agreement with the experimental (5.9 s) and other theoretical (6.14 s) results. Transition moment values of the spin allowed A(3)Π → X(3)Σ(-) transition have also been calculated at the same level of theory. Calculations show that the corresponding radiative lifetime is considerably low, 2.4 × 10(-7) s. Complete basis set extrapolated potential energy curves for the ground state of CH and the ground state and six low lying excited states (a(1)Δ, b(1)Σ(+), two (3)Π, and two (1)Π) of CH(-) are reported. These curves are then used to calculate the vibrational bound states for CH and CH(-). The computed electron affinity of CH supports the electron affinity bounds reported by Okumura et al. [J. Chem. Phys. 85, 1971 (1986)].

Energy loss distributions of He+ ions after collisions with HF molecules in a secondary beam at laboratory collision energies in the range 25–50 eV show a regular structure indicating rotational excitation up to ΔJ=35 with no clear evidence for vibrational excitation. The observed propensity for large ΔJ transitions decreases with increasing collision energy but increases with increase in scattering angle. Three dimensional quasiclassical trajectory calculations using a potential energy surface based on the He+–Ne interaction at short range and a damped long range ion–dipole (quadrupole) interaction reproduce all the essential features of the experimental results.

We report the results of a three-dimensional time-dependent quantum mechanical study of the reaction He + H 2 + (v = 0,1 ) → HeH+ + H at 〈Eintrans 〉 = 1.0 eV, which reproduces clearly the vibrational enhancement for the system. In addition, preliminary results for He + HD+ (v = 1–3) suggest the preferential formation of HeD+ over HeH+ in the products.

The effect of high initial vibrational (v = 0-25) and rotational (j = 0-100) excitation of the reactant molecule on the cross-section σR for the reaction Li2 + Na → LiNa + Li at a relative translational energy (E trans) of 0·5 eV has been investigated using the three-dimensional quasiclassical trajectory method on the recently proposed Varandas-Morais-Pais (VMP) potential. σR increases almost linearly with increase in v, but it remains unaltered, within the statistical error, with increase in j for j = 0-30. For the higher j states, there is an increase in σR with increase in j, and the rotational enhancement gets larger with increase in v, becoming comparable to the vibrational enhancement at v = 20. The dependence of σR on E trans over the range 0·18 - 0·85 eV has been examined for v = 0, j = 0. For E trans ⩽ 0·25 eV, all trajectories get trapped. For higher E trans, σR rises to a maximum and then levels off. Comparison of our results with those on the Whitehead-Grice (WG) potential reveals that the rea...

A three-dimensional time-dependent quantum mechanical wave packet approach is used to calculate reaction probability (P(R)) and integral reaction cross section (sigma(R)) values for both the channels of the reaction He + HD(+) (v = 1; j = 0, 1, 2, 3) --HeH(D)(+) + D(H), over a range of translational energy (E(trans)) on the McLaughlin-Thompson-Joseph-Sathyamurthy (MTJS) potential energy surface using centrifugal sudden approximation for nonzero total angular momentum (J) values. The reaction probability plots as a function of translational energy for different J values exhibit several oscillations, which are characteristic of the system. It is shown that HeH(+) is preferred over HeD(+) for large J values and that HeD(+) is preferred over HeH(+) for small J values for all the rotational (j) states studied. The integral reaction cross section for both the channels and therefore the isotopic branching ratio for the reaction depend strongly on j in contrast to the marginal dependence shown by earlier QCT calculations. The computed results are in overall agreement with the available experimental results.

pi-pi Interaction in pyridine dimer and trimer has been investigated in different geometries and orientations at the ab initio (HF, MP2) and DFT (B3LYP) levels of theory using various basis sets (6-31G, 6-31G, 6-311++G) and corrected for basis set superposition error (BSSE). While the HF and DFT calculations show the pyridine dimer and the trimer to be unstable with respect to the monomer, the MP2 calculations show them to be clearly stable, thus emphasizing the need to include electron correlation while determining stacking interaction in such systems. The calculated MP2/6-311++G binding energy (100% BSSE corrected) of the parallel-sandwich, antiparallel-sandwich, parallel-displaced, antiparallel-displaced, T-up and T-down geometries for pyridine dimer are 1.53, 3.05, 2.39, 3.97, 1.91, 1.47 kcal/mol, respectively. The results show the antiparallel-displaced geometry to be the most stable. The binding energies for the trimer in parallel-sandwich, antiparallel-sandwich, and antiparallel-displaced geometry are found to be 3.18, 6.14, and 8.04 kcal/mol, respectively.

Ab initio calculations suggest the possibility of forming boric acid clusters in the laboratory. The most stable form of the boric acid dimer contains two hydrogen bonds, similar to the carboxylic acid dimers. Though the trimer and the tetramer form extensions of this geometry, the pentamer prefers a bowl shape. Any addition of boric acid molecules to this geometry leads to bowl-shaped structures with the 15-mer forming a (3/4)buckyball and the 20-mer a full-fledged buckyball. The hexamer, on the other hand, prefers to stay planar as a hexagon-centered rosette. Any further extension of this geometry leads to planar structures as long as a pentagon is not included.

Fuller's earth (FE) has been used as an adsorbent in this work to remove mercury from aqueous solutions. For the purpose of comparison, simultaneous experiments using activated carbon (AC) have also been done. The aim of the work is to test how best FE can be used as an adsorbent for mercury. Equilibrium isotherms, such as Freundlich, Langmuir, Dubinin–Redushkevich, Temkin, Harkins–Jura, Halsey and Henderson have been tested. Kinetic studies based on Lagergren first-order, pseudo-second-order rate expressions and intra-particle diffusion studies have been done. The batch experiments were conducted at room temperature (30 °C) and at the normal pH (6.7 ± 0.2) of the solution. It has been observed that Hg(II) removal rate is better for FE than AC, due to large dosage requirement, whereas the adsorption capacity of AC is found to be much better than FE. Hence, although FE can be used as an adsorbent, a high dosage is required, when compared to AC. Hybrid fractional error function analysis shows that the best-fit for the adsorption equilibrium data is represented by Freundlich isotherm. Kinetic and film diffusion studies show that the adsorption of mercury on FE and AC is both intra-particle diffusion and film diffusion controlled.

Department of Chemistry, Indian Institute of Technology, Kanpur-208 016 We review some of our classical mechanical and quantum mechanical investigations of the reaction, He+ \(He_{2}^{+}\)+ HeH+ + H and its isotopic analog He + HD+ → HeH++D. HeD++H as well as the dissociative channel He+\(He_{2}^{+}\)→He+H+H+ over a wide range of translational energies for different vibrational states of \(He_{2}^{+}\)(HD+) while at the same time relating them to experimental and theoretical studies from other laboratories.