State-to-state chemistry and rotational excitation of CH+ in photon-dominated regions.

We present a detailed theoretical study of the rotational excitation of CH+ due to reactive and nonreactive collisions involving C+(2P), H2, CH+, H and free electrons. Specifically, the formation of CH+ proceeds through the reaction between C+(2P) and H2(νH2 = 1, 2), while the collisional (de)excitation and destruction of CH+ is due to collisions with hydrogen atoms and free electrons. State-to-state and initial-state-specific rate coefficients are computed in the kinetic temperature range 10-3000 K for the inelastic, exchange, abstraction and dissociative recombination processes using accurate potential energy surfaces and the best scattering methods. Good agreement, within a factor of 2, is found between the experimental and theoretical thermal rate coefficients, except for the reaction of CH+ with H atoms at kinetic temperatures below 50 K. The full set of collisional and chemical data are then implemented in a radiative transfer model. Our Non-LTE calculations confirm that the formation pumping due to vibrationally excited H2 has a substantial effect on the excitation of CH+ in photon-dominated regions. In addition, we are able to reproduce, within error bars, the far-infrared observations of CH+ toward the Orion Bar and the planetary nebula NGC 7027. Our results further suggest that the population of νH2 = 2 might be significant in the photon-dominated region of NGC 7027.

A theoretical study of the dissociative recombination of SH+ with electrons through the 2Π states of SH.

A quantitative theoretical study of the dissociative recombination of SH+ with electrons has been carried out. Multireference, configuration interaction calculations were used to determine accurate potential energy curves for SH+ and SH. The block diagonalization method was used to disentangle strongly interacting SH valence and Rydberg states and to construct a diabatic Hamiltonian whose diagonal matrix elements provide the diabatic potential energy curves. The off-diagonal elements are related to the electronic valence-Rydberg couplings. Cross sections and rate coefficients for the dissociative recombination reaction were calculated with a stepwise version of the multichannel quantum defect theory, using the molecular data provided by the block diagonalization method. The calculated rates are compared with the most recent measurements performed on the ion Test Storage Ring (TSR) in Heidelberg, Germany.

Absorption, autoionization, and predissociation in molecular hydrogen: High-resolution spectroscopy and multichannel quantum defect theory.

Absorption and photoionization spectra of H2 have been recorded at a resolution of 0.09 and 0.04 cm(-1), respectively, between 125,600 cm(-1) and 126,000 cm(-1). The observed Rydberg states belong to series (n = 10 - 14) converging on the first vibrationally excited level of the X (2)Σ(g)(+) state of H2(+), and of lower members of series converging on higher vibrational levels. The observed resonances are characterized by the competition between autoionization, predissociation, and fluorescence. The unprecedented resolution of the present experimental data leads to a full characterization of the predissociation/autoionization profiles of many resonances that had not been resolved previously. Multichannel quantum defect theory is used to predict the line positions, widths, shapes, and intensities of the observed spectra and is found to yield quantitative agreement using previously determined quantum defect functions as the unique set of input parameters.

Resonances in photoabsorption: predissociation line shapes in the 3pπD¹Π(u)⁺ ← X¹Σ(g)⁺ system in H2.

The predissociation of the 3pπD¹Π(u)⁺, v ≥ 3, N = 2, and N = 3 levels of diatomic hydrogen is calculated by ab initio multichannel quantum defect theory combined with a R-matrix type approach that accounts for interfering predissociation and autoionization. The theory yields absorption line widths and shapes that are in good agreement with those observed in the high-resolution synchrotron vacuum-ultraviolet absorption spectra obtained by Dickenson et al. [J. Chem. Phys. 133, 144317 (2010)] at the DESIRS beamline of the SOLEIL synchrotron. The theory predicts further that many of the D state resonances with v ⩾ 6 exhibit a complex fine structure which cannot be modeled by the Fano profile formula and which has not yet been observed experimentally.

Accumulation of three-body resonances above two-body thresholds.

We calculate resonances in the three-body system with attractive Coulomb potential by solving homogeneous Faddeev-Merkuriev integral equations for complex energies. The equations are solved using the Coulomb-Sturmian separable expansion method. This approach allows us to study the exact behavior of the three-body Coulomb systems near the threshold. A negatively charged positronium ion is used as a test case. In addition to locating all previously known S-wave resonances of the positronium ion, we also find a large number of new resonant states that accumulate just slightly above the two-body thresholds. The pattern of accumulation of resonant states above the two-body thresholds suggests that probably they are infinite in number. We conjecture that this may be a general property of the three-body system with an attractive Coulomb potential.

Stability study of prostacyclin in solution.

The proton-catalyzed hydrolytic decomposition of prostacyclin was assayed by UV spectroscopic and HPLC methods. Changes of the absorbance in aqueous solutions were measured at 220 nm. HPLC studies were performed on C18 column using NH4Cl (0.03 mol X l-1)/NH4OH (0.03 mol X l-1)/methanol (1 : 1 : 4) eluent. Temperature and pH dependence of the hydrolytic process was determined. Effects of alcohol and glycols on the degradation rate were studied.

A new method for high-performance liquid chromatographic determination of drotaverine in plasma.

A sensitive, specific high-performance liquid chromatographic procedure was developed for the determination of plasma drotaverine levels. Basic plasma samples were adjusted to pH 1.5 and extracted with chloroform. HPLC [n-heptane-dichloromethane-diethylamine (50:25:2)] on a microporous silica column, with a variable-wavelength UV detector set at 302 nm allowed the measurement of drotaverine at the 50-ng/mL level. The utility of this method for determination of drotaverine in dog and rat plasma was demonstrated.

Pharmacokinetic study of a new 1,2,4-oxadiazine derivative in rat.

Pharmacokinetics of 3-phenyl-6-(1, 2, 3, 4-tetrahydro-2-isoquinolyl)-methyl-4H-5,6-dihydro-1,2,4, -oxadiazine (I) in rat were studied. Plasma levels following a single oral dose were determined by HPLC method. Basic plasma samples were partitioned with chloroform. The organic layers were evaporated to dryness under reduced pressure. The residues were redissolved in chloroform and chromatographed on a microporous silica column with chloroform-isopropanol (7:3) eluent. Pharmacokinetics of (I) obeyed the one-compartment open model adequately. Constructed the plasma level curve, absorption and elimination rate constants were calculated by linear regression analysis. Rate of absorption proved to be significantly higher compared to that of elimination. The time of plasma level peak (tmax) was 35 min. After 20 h only traces of (I) could be found in the plasma.

High performance liquid chromatographic determination of a new biologically active 1,2,4-oxadiazine derivative in rat plasma.

A sensitive high performance liquid chromatographic procedure was developed for the determination of 3-phenyl-6-(1,2,3,4-tetrahydro-2-isoquinolyl)methyl-4H-5,6-dihydro -1,2, 4-oxadiazine a new vasodilator, in plasma. Rat plasma samples were made alkaline with ammonia and partitioned with chloroform. The extracts were dried with anhydrous sodium sulphate and evaporated to dryness under reduced pressure. The residues were redissolved in chloroform, and then chromatographed on silica column with chloroform/isopropanol (7:3, v/v). Detection was performed with a variable-wavelength UV detector set at 265 nm. Limit of identification was 10 ng, that of quantitative determination 50 ng 1/ml of plasma. The utility of the method for pharmacokinetic studies in the rat was demonstrated.