Acetylenic/cyanoacetylenic complexes: simulation of the Titan’s atmosphere chemistry

The structures and energies of the 1:1 acetylene/cyanoacetylene, acetylene/dicyanoacetylene and cyanoacetylene/dicyanoacetylene complexes in solid argon matrices have been investigated using FT-IR spectroscopy and ab initio calculations, at the B3LYP/6-31G** level of theory. For the three complexes, predicted frequency shifts for the L shaped structures, characterized by a hydrogen bond between the nitrogen of the cyano group and the acetylenic proton, were found to be in good agreement with those experimental. Only in the case of acetylene/cyanoacetylene complex, we obtained a second minimum with a T shaped structure characterized by an interaction between the proton of cyanoacetylene and the Π system of acetylene. It appears clearly that HC₃N acts as an electrophile or as a nucleophile in these complexes.     

Quasi-Periodic Solutions and Stability for a Weakly Damped Nonlinear Quasi-Periodic Mathieu Equation

Quasi-Periodic (QP) solutions are investigated for a weakly dampednonlinear QP Mathieu equation. A double parametric primary resonance(1:2, 1:2) is considered. To approximate QP solutions, a double multiple-scales method is applied to transform the original QP oscillator to anautonomous system performing two successive reductions. In a first step,the multiple-scales method is applied to the original equation to derive afirst reduced differential amplitude-phase system having periodiccomponents. The stability of stationary solutions of this reduced systemis analyzed. In a second step, the multiple-scales method is applied again tothe first reduced system (RS) to obtain a second autonomous differentialamplitude-phase RS. The problem for approximating QP solutions of theoriginal system is then transformed to the study of stationary regimesof the induced autonomous second RS. Explicit analytical approximationsto QP solutions are obtained and comparisons to numerical integrationare provided.     

UV photolysis of C4N2 in water ices: new possible route of synthesis of ammonium bicarbonate and ammonium formate

Laboratory experiments involving ultraviolet (UV) irradiation of dicyanoacetylene (C(4)N(2)) trapped in water ice at 10 K have been conducted and monitored by infrared spectroscopy (FTIR). By the support of isotopic experiments and theoretical calculations, the irradiation of a DCA/H(2)O ice mixture at lambda > 230 nm has been found to be a possible source of NH(4)(+)HCO(3)(-) (ammonium bicarbonate) and NH(4)(+)HCOO(-) (ammonium formate). These latter compounds can arise from a proton-transfer reaction between H(2)O and the CN radical, which is issued from photolyzed C(4)N(2).     

The electronic gas-phase spectrum of B3 radical revisited

The gas-phase electronic spectrum of cyclic-B₃ (D_3h) radical has been remeasured in a supersonic molecular beam using a mass-selective resonant 2-color 2-photon technique, leading to a revision of previously reported spectroscopic constants. The species was prepared by ablation of a boron nitride rod in the presence of helium. Ab intio calculations on the geometries and vertical electronic excitation energies, as well as mass identification, indicate that the detected band, centered at 21848.77(2) cm⁻¹, is the origin of the cyclic-¹¹B₃ system. A spectral fit yields the rotational constants as B″ = 1.2246(45) and C″ = 0.62131(72) cm⁻¹ in the ground state, and B′ = 1.1914(44) and C′ = 0.61173(69) cm⁻¹ in the excited 2 ²E′ state.     

Molecular geometry and vibrational studies of 3,5-diamino-1,2,4-triazole using quantum chemical calculations and FT-IR and FT-Raman spectroscopies

The 3,5-diamino-1,2,4-triazole (guanazole) was investigated by vibrational spectroscopy and quantum methods. The solid phase FT-IR and FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3600-50 cm(-1) respectively, and the band assignments were supported by deuteration effects. The results of energy calculations have shown that the most stable form is 1H-3,5-diamino-1,2,4-triazole under C1 symmetry. For this form, the molecular structure, harmonic vibrational wave numbers, infrared intensities and Raman activities were calculated by the ab initio/HF and DFT/B3LYP methods using 6-31G* basis set. The calculated geometrical parameters of the guanazole molecule using B3LYP methodology are in good agreement with the previously reported X-ray data, and the scaled vibrational wave number values are in good agreement with the experimental data. The normal vibrations were characterized in terms of potential energy distribution (PEDs) using VEDA 4 program.     

Interior-point methods for linear optimization based on a kernel function with a trigonometric barrier term

In this paper, we present a new barrier function for primal–dual interior-point methods in linear optimization. The proposed kernel function has a trigonometric barrier term. It is shown that in the interior-point methods based on this function for large-update methods, the iteration bound is improved significantly. For small-update interior-point methods, the iteration bound is the best currently known bound for primal–dual interior-point methods.     

Photochemistry of coronene with water at 10 K: first tentative identification by infrared spectroscopy of oxygen containing coronene products

UV photochemistry of a polycyclic aromatic hydrocarbon model, coronene (C(24)H(12)), has been investigated when it is in interaction with water in argon cryogenic matrices, adsorbed on amorphous water ice films, and embedded in solid water. Photoprocessing, carried out at 10 K and λ > 235 nm by means of a high-pressure Hg arc lamp, results in the oxidation and reduction of coronene. These species have been tentatively identified as being the 1,10-dihydroxycoronene and the 1,10-coroquinone by FTIR spectroscopy with the support of isotopic experiments and DFT calculations. These photochemical products most likely form, after hydrogen bonding between C(24)H(12) and H(2)O, through ionization of the PAH and subsequent reactivity with water upon irradiation. Cations, thus generated, react subsequently with water yielding the production of oxygen containing coronene compounds. Such species are of particular interest as they may form in interstellar and early Solar System ices, and are also of astrobiological significance as they could play an important role in processes taking place in most of the living organisms.     

Photochemistry of pyrene with water at low temperature: study of atmospherical and astrochemical interest

Photochemistry of a polyaromatic hydrocarbon, pyrene C(16)H(10), with water has been investigated at cryogenic temperatures. Photoprocessing of this species, performed at λ > 235 nm, in argon matrices, adsorbed onto amorphous water surfaces, and trapped in solid water, led to the formation of ketonic isomers, C(16)H(10)O, and possibly quinones. These species have been identified for the first time by infrared spectroscopy with the support of isotopic substitution experiments and DFT calculations. These oxidized pyrene-like species, of atmospherical and astrochemical interest, most likely arise from a tautomeric rearrangement of their analogous hydroxylated molecules, these latter being formed by reaction of water with pyrene cations.     

2:2:1 Resonance in the Quasiperiodic Mathieu Equation

In this work, we investigate regions of stability in the vicinity of 2:2:1 resonance in the quasiperiodic Mathieu equation $$\frac{{d^2 x}}{{dt^2 }} + \left( {\delta + \varepsilon \cos t + \varepsilon \mu \cos \left( {1 + \varepsilon \Delta } \right)t} \right)x = 0,$$ using two successive perturbation methods. The parameters ∈ andμ are assumed to be small. The parameter ∈ serves forderiving the corresponding slow flow differential system and μserves to implement a second perturbation analysis on the slow flowsystem near its proper resonance. This strategy allows us to obtainanalytical expressions for the transition curves in the resonantquasiperiodic Mathieu equation. We compare the analytical results withthose of direct numerical integration. This work has application toparametrically excited systems in which there are two periodicdrivers, each with frequency close to twice the frequency of theunforced system.