Structural aspects of crown complexes with alkali and alkaline earth cations. Benzo-15-crown-5 as a discriminating macrocycle

X-ray structural results have been reviewed for the related M^z+ L _z ^– -B15C5 complexes where M^z+=Li⁺ to Cs⁺ and Mg²⁺ to Ba²⁺, L^–=2,4,6-trinitrophenolate (Picrate or Pic) and 3,5-dinitrobenzoate (Dnb), and B15C5=benzo-15-crown-5. These results combined with those for come MX_z-B15C5 (X=NCS^–, I^–, NO ₃ ^– , ClO ₄ ^– , BPh ₄ ^– ) complexes have revealed that B15C5 is a useful macrocycle with regard to the within-the-group and between-the-groups discriminations of M^z+ in the solid state.     

Ultrafast relaxation and coherent oscillations in aminobenzonitriles in the gas phase probed by intense-field ionization

4-Aminobenzonitrile derivatives have two excited states of similar energy: besides the benzene-like L(b) state (also termed "locally excited" or LE state) one with charge-transfer (CT) character that is slightly higher in the isolated molecules. The CT state can be lowered by solvents of suitable polarity, so that dual fluorescence can be observed in them. It is controversial along which coordinate this state is displaced, although the amino-group twist is a wide-spread assumption. We investigated a number of such compounds by transient ionization in the gas phase, initially exciting the higher-lying L(a) state (S(2)). Here we briefly review the previous results on 4-(dimethylamino)benzonitrile (the prototype of this class of molecules), 4-piperidino-, pyrrolidino- and pyrrolyl-benzonitrile and compare them with new results on 4-aminobenzonitrile and on the bridged derivative N-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6). Although in the latter two molecules the CT state has never been detected before, we find the same relaxation path for all compounds: From S(2), the wave packet passes through a conical intersection (CI); from there part of it reaches the S(1) (L(b)) state directly, whereas another part temporarily populates the CT state (also in NMC6), from where it goes around the CI also to the L(b) well. The wave packet directly reaching the L(b) well oscillates there along coordinates involving amino-group twist and wagging or molecular arching and a quinoidal distortion. These coordinates must be components of the CI displacement vector. A vibration involving bond-length alternation of the benzene ring is ascribed to a momentum caused by the electronic symmetry change in the CI, i.e., to the nonadiabatic coupling vector. Also the CT state involves amino-group twist, as to conclude from the anisotropy of the corresponding signal. The six-membered aliphatic ring in NMC6 hinders the twist and raises the CT state to an energy that is, however, still below the L(a) state, so that it can be temporarily populated in a barrierless process. Also in aminobenzonitrile the CT state is between L(a) and L(b) and is reached from L(a) without a barrier. The twist is rationalized by vibronic interaction with a higher state that is pi-antibonding between the amino group and the aromatic ring.     

Comparison of 1 MeV electron,Co-60 gamma and 1 MeV proton irradiation effects on silicon NPN transistors

The total dose effects of 1?MeV electrons on the dc electrical characteristics of silicon NPN transistors are investigated in the dose range from 100?krad to 100?Mrad. The different electrical characteristics such as Gummel characteristics, excess base current (ΔI_B), dc current gain (h_FE), transconductance (g_m), displacement damage factor (K) and output characteristics were studied in situ as a function of total dose. A considerable increase in base current (I_B) and a decrease in h_FE, g_m and I_CSat was observed after 1?MeV electron irradiation. The collector–base (C–B) junction capacitance of transistors was measured to estimate the change in the effective carrier concentration. After 1?MeV electron irradiation, a considerable degradation in capacitance was observed. The plot of (1/C²) versus voltage shows that the effective carrier concentration and built-in voltage (V_bi) increase marginally upon 1?MeV electron irradiation. The results of 1?MeV electron irradiation were compared with 1?MeV proton and Co-60 gamma irradiation results in the same dose range. The degradation for 1?MeV electron and Co-60 gamma-irradiated transistors was significantly less when compared to 1?MeV proton-irradiated transistor. The 1?MeV proton, 1?MeV electron and Co-60 gamma-irradiated transistors were subjected to isochronal annealing to analyze the recovery of the electrical parameters.     

Asymptotic solution of a non-linear wave motion in an electron plasma

The theory of high-frequency waves has been used to calculate first and second-order asymptotic solutions for the propagation of non-linear waves in a cylindrical symmetric flow of an electron plasma. The behaviour of acceleration waves and weak shock waves has been analysed through these solutions and Whitham's rule for a weak shock wave on any wavelet has been confirmed through the first-order solution. The appearance of a weak shock wave on any wavelet has been determined and its strength, the location, and the speed of propagation have been found from the asymptotic solution presented in this paper. © 1997 by B. G. Teubner Stuttgart–John Wiley & Sons Ltd.     

Comparison of effect of 5 MeV proton and Co-60 gamma irradiation on silicon NPN rf power transistors and N–channel depletion MOSFETs

NPN transistors and N-channel depletion metal oxide semiconductor field effect transistors (MOSFETs) were irradiated with 5?MeV protons and ⁶⁰Co gamma radiation in the dose ranging from 1?Mrad(Si) to 100?Mrad(Si). The different electrical characteristics of the NPN transistor such as Gummel characteristics, excess base current (ΔI_B), dc current gain (h_FE), transconductance (g_m), displacement damage factor (K) and output characteristics were studied as a function of total dose. The different electrical characteristics of N-channel MOSFETs such as threshold voltage (V_th), density of interface trapped charges (ΔN_it), density of oxide trapped charges (ΔN_ot), transconductance (g_m), mobility (µ) and drain saturation current (I_DSat) were studied systematically before and after irradiation in the same dose ranges. A considerable increase in the base current (I_B) and decrease in the h_FE, g_m and collector saturation current (I_CSat) were observed after irradiation in the case of the NPN transistor. In the N-channel MOSFETs, the ΔN_it and ΔN_ot were found to increase and V_th, g_m, µ and I_DSat were found to decrease with increase in the radiation dose. The 5?MeV proton irradiation results of both the NPN transistor and N-channel MOSFETs were compared with ⁶⁰Co gamma-irradiated devices in the same dose ranges. It was observed that the degradation in 5?MeV proton-irradiated devices is more when compared with the ⁶⁰Co gamma-irradiated devices at higher total doses.     

Zwitterionic‐Type Molten Salt‐Catalyzed Multicomponent Reactions: One‐Pot Synthesis of Substituted Imidazoles Under Solvent‐Free Conditions

4‐(1‐Imidazolium) butane sulfonate is an excellent catalyst for the synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles through the condensation of 1,2‐dicarbonyl compounds, aldehydes, and ammonium acetate or amine via multicomponent condensation strategy under solvent‐free conditions. The key advantages of this process are high yields, reusability of catalyst, environmental friendliness, easy work‐up and purification of products by nonchromatographic methods.     

Rate constants for the gas‐phase reactions of chlorine atoms with 1,4‐cyclohexadiene and 1,5‐cyclooctadiene at 298 K

Rate constants for the reactions of Cl atoms with two cyclic dienes, 1,4‐cyclohexadiene and 1,5‐cyclooctadiene, have been determined, at 298 K and 800 Torr of N₂, using the relative rate method, with n‐hexane and 1‐butene as reference molecules. The concentrations of the organics are followed by gas chromatographic analysis. The ratios of the rate constants of reactions of Cl atoms with 1,4‐cyclohexadiene and 1,5‐cyclooctadiene to that with n‐hexane are measured to be 1.29 ± 0.06 and 2.19 ± 0.32, respectively. The corresponding ratios with respect to 1‐butene are 1.50 ± 0.16 and 2.36 ± 0.38. The absolute values of the rate constants of the reaction of Cl atom with n‐hexane and 1‐butene are considered as (3.15 ± 0.40) × 10^?10 and (3.21 ± 0.40) × 10^{? 10} cm³ molecule^?1s^?1, respectively. With these, the calculated values are k(Cl + 1,4‐cyclohexadiene) = (4.06 ± 0.55) × 10^?10 and k(Cl + 1,5‐cyclooctadiene) = (6.90 ± 1.33) × 10^?10 cm³ molecule^?1 s^?1 with respect to n‐hexane. The rate constants determined with respect to 1‐butene are marginally higher, k(Cl + 1,4‐cyclohexadiene) = (4.82 ± 0.80) × 10^{? 10} and k(Cl + 1,5‐cyclooctadiene) = (7.58 ± 1.55) × 10^{? 10} cm³ molecule^?1 s^?1. The experiments for each molecule were repeated three to five times, and the slopes and the rate constants given above are the average values of these measurements, with 2σ as the quoted error, including the error in the reference rate constant. The relative rate ratios of 1,4‐cyclohexadiene with both the reference molecules are found to be higher in the presence of oxygen, and a marginal increase is observed in the case of 1,5‐cyclooctadiene. Benzene is identified as one major product in the case of 1,4‐cyclohexadiene. Considering that the cyclohexadienyl radical, a product of the hydrogen abstraction reaction, is quantitatively converted to benzene in the presence of oxygen, the fraction of Cl atoms that reacts by abstraction is estimated to be 0.30 ± 0.04. The atmospheric implications of the results are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 431–440, 2011     

High efficiency nanotextured silicon solar cells

We report the computational modeling of forward scattering phenomena arising in Au nanoparticles array near their localized surface plasmon resonance, which by producing a strong field enhancement effect on the substrate leads to higher optical absorption and, therefore, higher efficiencies of operation. Computational calculations indicate that the ultimate efficiency of an optimized silicon nanoholes (SiNH) array texture surface in combination with the surface and bottom-of-a-trench Au nanoparticles array described herein, is 39.67%, which compares favorably with the ultimate efficiency of 31.11% for an optimized silicon nanoholes array texture surface. Furthermore, the utilization of an optimized silicon nitride antireflection coating increases the ultimate efficiency to a promising value of 41.88%, while the utilization of a single-crystal silicon layer of thickness 2.8 μm will be instrumental in drastically reducing solar cell manufacturing cost.     

Synthesis and Properties of the Alkyl/Aryl Germanium Dioximates Containing Ge─O Bond: Stability Factors—A Theoretical Approach

The reactions of R₂GeCl₂ and R₃GeCl with 9,10‐phenanthrenequinone dioxime in 1:1 and 1:2 molar ratios to form a series of organogermanium complexes of the general formula R₂GeL and (R₃Ge)₂L [R=Me, Et, Ph] have been investigated. The physical and spectral properties of all derivatives are described. In addition, the nature of Ge─O bond has been studied by using the DFT/B3LYP method.