An analytical representation of the ground potential energy surface (2A') of the H + Cl2 → HCl + Cl and Cl + HCl → HCl + Cl reactions, based on ab initio calculations

In this work we have studied at an ab initio level the lowest 2A′ potential energy surface (PES) of the HCl2 system. This PES is involved in the H(2S)+Cl2(X 1Σ+g)→HCl(X 1Σ+)+Cl(2P) and Cl(2P)+HCl(X 1Σ+)→HCl(X 1Σ+)+Cl(2P) gas phase elementary chemical reactions. The former reaction is an important chemical laser while the second one is the most frequently used prototype of heavy-light-heavy reaction. A large number of points on the 2A′ PES have been calculated at the PUMP2/6-311G(3d2 f,3p2d) ab initio level. The ab initio calculations show the existence of two angular transition states with negligible or very small barriers to collinearity. This and other properties of the PES are in agreement with previous studies. An analytical expression based on a many-body expansion has been used to obtain a satisfactory fit of the 740 ab initio points calculated, with a root-mean-square deviation within the range of the estimated ab initio method error margin. This analytical representation of the 2A′ PES has been used to evaluate the variational transition state theory thermal rate constants of the above-mentioned reactions, including also the Cl+DCl reaction, and quite good agreement has been obtained when comparing with experimental results. The analytical PES obtained in this work is suitable for use in studies on the kinetics and dynamics of the HCl2 system

An ab initio analytical potential energy surface for the O(3P) + CS(X1Σ+) → CO(X1Σ+) + S(3P) reaction useful for kinetic and dynamical studies

The N(4Su) + NO(X 2Π) → N 2(X 1Σg+) + O( 3Pg) reaction plays an important role in the upper atmosphere chemistry and as a calibration system for discharge flow systems. Surprisingly, very little theoretical and experimental work has been devoted to the characterization of the dynamical features of this system. In this work a Sorbie-Murrell expression for the lowest 3A″ potential energy surface (PES) connecting reactants in their ground electronic states based upon the fitting of an accurate ab initio CI grid of points has been derived. The PES fitted shows no barrier to reaction with respect to the reactants asymptote in accordance with experimental findings and becomes highly repulsive as the NNO angle is varied away from the saddle point geometry. The results of preliminary quasiclassical trajectory calculations on this surface reproduce very well the experimental energy disposal in products, even though the vibrational distribution derived from trajectories seems to be a bit cooler than the experimental data. Moreover, thermal rate constants derived from trajectories are in excellent accordance with experimental value

Ab initio 1A' ground potential energy surface and transition state theory kinetics study of the O(1D) + N2O → 2NO, N2 +O2(a1Δg) reactions

An ab initio study of the 1A' ground potential energy surface (PES) of the O(1D) + N2O(X1+) system has been performed at the CASPT2//CASSCF (complete active space second-order perturbation theory//complete active space self-consistent field) level with Pople basis sets. The two reactions leading to 2 NO(X2) [reaction (1)] and N2(X1g+) + O2(a1∆g) [reaction (2)] products have been investigated. In both reactions a trans-approach of the attacking oxygen to the N2O moiety is found to be preferred, more markedly in reaction (1). For this reaction also a cis-path is feasible and is possibly connected with the trans -path by a transition state placed below reactants. A thorough characterization of the entrance zone has been performed to allow for subsequent kinetics calculations. Fixed angle and minimum energy paths have been constructed and transition state geometries have been refined at the CASPT2 level, thus obtaining approximate structures and frequencies for the latter. From these calculations it can be inferred that both reactions proceed without an energy barrier. Rate constant calculations in the 100-1000 K temperature range based on CASPT2 structures and using the transition state theory yield values in good agreement with experiment for the two reactions, especially when a proper scaling of the energy barriers is performed. Also, for comparative purposes quasiclassical trajectory calculations were performed on reaction (1) in the same temperature range, using a previous pseudotriatomic analytical potential energy surface, obtaining good agreement with experiment

Theoretical investigation of the eight low-lying electronic states of the cis- and trans-nitric oxide dimers and its isomerization using multiconfigurational second-order perturbation theory (CASPT2)

In this work we have carried out ab initio electronic structure calculations, CASSCF/CASPT2 and CASSCF/MRCI-SD+Q with several Pople's and correlation-consistent Dunning's basis sets, of the planar cis- and trans-NO dimers for the lowest eight electronic (singlet and triplet) states. The geometry, frequencies, dipole moment, binding energy, and vertical excitation energies are predicted with an accuracy close to or even better than the best reported ab initio previous results for some of these properties, and in very good agreement with the available experimental data. CASPT2 optimized geometries show the existence of at least four shallow NO-dimers (i.e., two cis-(NO)2 (1A1 and 3B2) and two trans-(NO)2 (1Ag and 3Au)), although CASSCF optimization with CASPT2 pointwise calculations indicate the existence of other less stable dimers, on the excited states. Vertical excitation energies were calculated for these four dimers. For the cis-NO dimer, the ordering and the energy spacings between the excited states (i.e., 1A1, 3B2, 1B2, 2nd 1A1, 1A2, 3A2, 3B1, 2nd 3B1) are very similar to those found in a recent MRCI-SD study. The singlet cis-NO dimer (1A1) is the most stable one in almost quantitative accord with the experimental data, and in disagreement with previous density functional theory studies. A nonplanar transition state for the singlet trans ↔ cis isomerization has also been fully characterized. This leads to an almost negligible energy barrier which would originate a rapid isomerization to the most stable cis-NO dimer at low temperatures, in accord with the experimental difficulties to measure the properties of the trans-NO dimer. Not only are basis set superposition error corrections necessary to evaluate accurately the binding energies, but also to determine the NN distance of these symmetrical dimers. Some problems regarding the symmetry of the wave function were found for the symmetrical NO dimers and for the NO+NO asymptote, and several approximate solutions were proposed

Influence of the collision energy on the O(1D) + RH --> OH(X2Pi) + R (RH=CH4, C2H6, C3H8) Reaction Dynamics. A laser Induced Fluorescence and Quasiclassical Trajectory Study

The influence of the collision energy (ET) on the O(1D) + RH OH(X2H) + R (RH = CH4, C2H6, and C3H8) reaction dynamics has been studied, using the N2O photodissociation at 193 nm as O(1D) precursor (ET = 0.403 eV) and probing the OH v = 0 and 1 levels by LIF. A triatomic QCT study of the reaction with CH4 on a fully ab initio based analytical PES has also been performed, and a quite good agreement with the experimental OH rovibrational distributions has been obtained. Our experimental results are similar to those obtained when the O3 photodissociation is used to produce O(1D) (ET = 0.212 eV), as expected on the basis of the available energy in products and also from the QCT calculations. The P(v=0)/P(v= 1) populations ratio values reported for C2H6 and C3H8 in a very recent work (Wada and Obi, J. Phys. Chem. A 1998, 102, 3481), where the N2O was also used to generate O(1D), are probably largely underestimated. The rotational distributions obtained are similar to those obtained in other experiments, and a quite good agreement has been obtained for the spin-orbit and A-doublet populations. The reaction takes place near exclusively through the insertion of the O(1D) atom into a C-H bond below 0.6 eV, and the mechanism may be direct or nondirect (mainly through short-lived (CH3)OH collision complexes) with about the same probability. The OH vibrational distribution arising from the direct mechanism is inverted, while the nondirect one leads to a noninverted distribution. At higher ET, the abstraction mechanism also contributes appreciably to reactivity. © 2000 American Chemical Society

Stereodynamical studies of velocity aligned photofragments

The state resolved stereodynamics of bimolecular reactions can be probed using velocity aligned photofragments as reagents, and polarised, Doppler resolved laser detection techniques for the products. The new strategy and its application to the reaction O(1D) + N2O→ NO + NO are outlined

Zileuton™ loaded in polymer micelles effectively reduce breast cancer circulating tumor cells and intratumoral cancer stem cells

Tumor recurrence, metastatic spread and progressive gain of chemo-resistance of advanced cancers are sustained by the presence of cancer stem cells (CSCs) within the tumor. Targeted therapies with the aim to eradicate these cells are thus highly regarded. However, often the use of new anti-cancer therapies is hampered by pharmacokinetic demands. Drug delivery through nanoparticles has great potential to increase efficacy and reduce toxicity and adverse effects. However, its production has to be based on intelligent design. Likewise, we developed polymeric nanoparticles loaded with Zileuton™, a potent inhibitor of cancer stem cells (CSCs), which was chosen based on high throughput screening. Its great potential for CSCs treatment was subsequently demonstrated in in vitro and in in vivo CSC fluorescent models. Encapsulated Zileuton™ reduces amount of CSCs within the tumor and effectively blocks the circulating tumor cells (CTCs) in the blood stream and metastatic spread

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N2, O2, NO), Mars (CO2, CO, N2) and Jupiter (H2, He) atmospheres are considered

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N-2, O-2, NO), Mars (CO2, CO, N-2) and Jupiter (H-2, He) atmospheres are considered