Electronic spectra of linear isoelectronic species HC6H+, C6H, HC5N+

Multireference configuration interaction calculations have been used to determine term energies of low-lying doublet electronic states of isoelectronic carbon chains HC6H+, C6H and HC5N+. Calculations on relevant excited states in the energy range up to 6 eV show that (2)Pi and (2)Phi excited states due to the pi-pi excitation are comparable in energy pattern among such species, but that there are significant differences in the properties of (2)Sigma and (2)Delta excited state series of these isoelectronic species. Similarities and discrepancies are discussed based on molecular orbital energy patterns and electron correlation. The strongest transitions for HC6H+, C6H and HC5N+ are predicted to correspond to X(2)Pi -->2(2)Pi transitions at 2.22, 2.56 and 2.17 eV, respectively. For HC6H+, no (2)Sigma or (2)Delta states arising from sigma-pi electron promotion are found in the energy range up to 6 eV. However, in C6H the first excited state 1(2)Sigma (+) due to the 13 sigma -->3 pi excitation is found to be only slightly higher (0.22 eV) than the ground state X(2)Pi. Calculated transition energies in the present study show good agreement with available experimental results

Low-lying electronic states and molecular structure of Fe2O2

The structure, bonding and relative stabilities of the ground and low-lying excited states of Fe2O2 have been studied by the hybrid B3LYP density-functional and coupled-cluster molecular orbital methods. Calculations indicate that the (mu-O)(2) rhombic B-7(2u) State is the ground state for Fe2O2. Stable molecular diiron oxo Fe-2-O-2 complexes in distorted tetrahedral and planar side-on modes have been also located on the potential-energy hypersurfaces of Fe2O2. The calculated IR-active frequencies corresponding to two in-plane deformations of the rhombic ring agree well with the observed values. The bonding features of the (mu-O)(2) rhombic Fe2O2 have been discussed based on natural bond orbital and Bader topological analyses. These analyses show that an effective Fe-Fe bonding across the ring exists in the B-7(2u) ground state

Size dependence of electronic excitation energy in linear C2nH and C2n-1N

The geometries, bondings, and vibrational frequencies of C2nH (n=3-9) and C2n-1N(n=3-9) were investigated by means of density functional theory (DFT). The vertical excitation energies for the (XII)-I-2-->(II)-I-2 transitions of C2nH(n=3-9) and for the X(2)Sigma-->(II)-I-2 and the (XII)-I-2-->(II)-I-2 transitions of C2n-1N(n=3-9) have been calculated by the time-dependent density functional theory (TD-DFT) approach. On the basis of present calculations, the explicit expression for the wavelengths of the excitation energies in linear carbon chains is suggested, namely, lambda(0) = [1240. 6A/(2 + root3n+6 - root3n+3)] (1 - Be-Cn), where A = 3.24463, B = 0.90742, and C = 0.07862 for C2nH, and A = 2.94714, B = 0.83929, and C=0.08539, for C2n-1N. In consideration of a comparison of the theory with the experiment, both the expressions are modified as lambda(1) = 0. 92 (lambda(0) +100) and lambda(1) = 0. 95(lambda(0)+90) for C2nH and C2n-1N, respectively

MULTI-WAVELENGTH EMISSIONS FROM THE MILLISECOND PULSAR BINARY PSR J1023+0038 DURING AN ACCRETION ACTIVE STATE

published_or_final_versio

Theoretical studies on structures and spectroscopic properties of nitryl halogenides

Density functional theory with the B3LYP functional is used to calculate the equilibrium geometries and harmonic vibrational frequencies of nitryl halogenides XNO2 and XONO (X = F, Cl, Br, I). Stabilities and isomerizations of these isomers are investigated. Dissociation energies of the X-N bond in XNO2 are predicted at the B3LYP/6-311G* and QCISD(T)/ce-pvTZ levels. The electronic transition energies of the most stable XNO2 species have been estimated by time-dependent B3LYP calculations. The electron promotion of a nonbonding electron of the halogen atom X in XNO2 into a pi* orbital on the NO2 moiety, i.e., the n-->sigma* electron excitation, is responsible for the photodissociation of the X-N bond

Valence bond study of dissociation behavior and spectroscopic constants for the ground states of LiF and NaF

Ab initio VB calculations were used to determine the accurate spectroscopic parameters of the ground stated of LiF and NaF. A set of potential energy curves corresponding to the ground states including ionic and covalent interactions, pure ionic interaction and covalent interaction were generated using the VBSCF method. Curve crossing in the dissociation processes of LiF and NaF was discussed. The optimized VB wave functions suggest that LIF and NaF are of high ionicity, and their ionic weights are 86.2% and 94.6%, respectively. NaF has a higher ionicity. The main difference between atom F and ion F- and the effect of the proper description of this difference on dissociation energies were investigated

Variations of Particle Size Distribution, Black Carbon, and Brown Carbon during a Severe Winter Pollution Event over Xi'an, China

Real-time particulate matter (PM) size distributions, 4-hour time resolution, PM2.5, carbonaceous materials, and their optical properties were measured during a severe pollution event in Xi'an, China High PM2.5 /PM10 ratios were observed on both pollution (0.83) and non-pollution (0.73) days, emphasizing the abundance of fine particles during sampling days. The particle number (PN) first peaked with a wide size range (30-100 nm) before morning rush hours (approximately 01:00-05:00) on pollution and non-pollution days, demonstrating that PN was governed by the accumulation of freshly emitted diesel particles and characterized by distinct aerosol condensation growth. By contrast, the second peak time and size range differed between pollution and non-pollution days because of different formation mechanisms The light-absorbing coefficients of both black carbon (BC, b(abs-880nm,BC)) and brown carbon (BrC, b(abs-370nm, BrC)) were high on pollution days and decreased to approximately half of those values on non-pollution days, indicating that the degree of light absorption is reduced by rain. The diurnal variation in b(abs-880nm, BC) pollution peaked with traffic on January 1 and 2. By contrast, it remained in relatively stable and high ranges (120-160 Mm(-1)) in the second period (January 3-5) without traffic peaks, illustrating that the dominant sources changed even during the same pollution period. High values of both b(abs-370nm, BrC) and b(abs-880nm,) (BC )coincided in the afternoon and evening due to emissions from primary sources, and abundant aqueous secondary organic carbon, respectively. A highly variable mass absorption coefficient of BrC also indicated the variety of fuel combustion sources of primary BrC in Xi'an

3D Printed Polypropylene Continuous-Flow Column Reactors: Exploration of Reactor Utility in SNAr Addition Reactions and the Synthesis of Bicyclic and Tetracyclic Heterocycles

3D printing has the potential to transform the way in which chemical reactions are carried out due to its low-cost, ease-of-use as a technology and its capacity to expedite the development of iteratively enhanced prototypes. In this present study, we developed a novel, low-cost polypropylene (PP) column reactor that was incorporated into an existing continuous-flow reactor for the synthesis of heterocycles. The utility and solvent resistance of the printed devices were explored in SNAr reactions to produce substituted aniline derivatives and in the synthesis of bicyclic and tetracyclic heterocycles. Using this approach, a range of heterocyclic compounds was synthesised including the core structure of the natural product (±)-γ-lycorane and structurally complex compounds based on the tetracyclic core of the erythrina alkaloids