Na clusters bound to mica surfaces have been irradiated with pulsed and cw visible laser light. Kinetic energy and angular distributions of the Na atoms desorbing from the clusters have been determined using cw two-photon laser-induced fluorescence detection. In addition the dependence of the desorption rate on laser power, wavelength and polarization has been measured. The most probable kinetic energyEkin of the photodesorbed atoms at the surface temperatureTS=300 K was found to beEkin=18±5 meV, independent of laser irradiance (3 µJ/cm2...20 mJ/cm2) and wavelength (450 nm, 505 nm, 658 nm). With increasing orientation angle between detection axis and surface normal (0°≦Θ≦90°)Ekin was observed to decrease slightly, while it was nearly independent of surface temperature betweenTS=30 K andTS=300 K. Also, with increasing radius of the Na clusters the desorbing Na atoms slowed down. The angular distribution of the Na atoms was of cos2-type with respect to the surface normal. These observations suggest that laser-induced desorption of Na from Na clusters bound to mica surfaces involves an initial rate-limiting step of direct surface plasmon excitation followed by a final step of delayed thermal desorption. 相似文献
A fast and simple method for simultaneous detection and quantification of the medicinally important E- and Z-guggulsterone from raw oleogum-resin of Commiphora wightii by UPLC was developed. Both E- and Z-guggulsterone were extracted from naturally occurring resin samples using ethyl acetate and methanol. Chromatographic separation of the analytes and their respective standards were performed on an Acquity UPLC BEH C18 column followed by UV as well as a triple quadrupole detector in positive ionization mode. A linear gradient elution profile followed; mobile phase consisted of acetonitrile and 2 mM ammonium acetate in water. The method was validated over a range of 6.25 to 100 ng mL?1 for both the guggulsterones. The calibration curves were linear with correlation coefficients of 0.9998 for E-guggulsterone and 0.9999 for Z-guggulsterone. The LOD and LOQ were 1.65 and 5.02 ng mL?1 for E-guggulsterone and 2.57 and 7.79 ng mL?1 for Z-guggulsterone respectively. The average recovery of E-guggulsterone (104.63%) and Z-guggulsterone (104.33%) achieved from spiked samples were consistent and reproducible. The intra- and inter-day assay precision of the analytes over the entire concentration range was less than 2%. The developed method required only 6 min to complete a run including 1 min to equilibrate the system and hence suitable for high throughput applications. Efficiency, reliability and accuracy of the developed method were evaluated by analyzing resin sample from different C. wightii populations. The result of this study offers improvement in terms of speed and sensitivity as compared to previously reported methods. 相似文献
Reactive scattering of O atoms with CF3I molecules has been studied at an initial translational energy E = 32.1 kJ mol?1 using a He seeded O atom beam and at E = 13.9 kJ mol?1 using a Ne seeded O atom beam. Reactive scattering of IO product favours the backward hemisphere at low energy but becomes almost isotropic at high energy. The product translational energy distribution at low energy indicates substantial energy transfer with internal modes of the collision complex but at high energy the excess energy is disposed into product translation. 相似文献
A least-squares linear-Taylor differential-correction technique has been used for the rapid evaluation of thermogravimetric curves obtained during the decomposition of magnesium hydride, iron—titanium hydride and lanthanum—nickel hydride. For magnesium hydride and iron—titanium hydride the Avrami—Erofe'ev equation fits the experimental data, thus indicating that nucleation is the rate-determining step under thermogravimetric conditions. For lanthanum—nickel hydride a combination of the Avrami—Erofe'ev equation and the phase boundary movement equation fits the data up to a fractional decomposition of 0.8. For magnesium hydride decomposition the activation energy E and the pre-exponential factor Z are dependent on the hydrogen pressure (E = 101.2 kJ mole?1 and Z = 8.96 × 107 at 0.30 MPa, while E = 66.3 kJ mole?1 and Z = 4.77 × 107 at 0.11 MPa). For iron—titanium hydride (E = 28.4 kJ mole?1) and lanthanum—nickel hydride (E = 13.4 kJ mole?1) the values are independent of pressure. 相似文献
Reaction of E- and Z-4-chlorohept-3-enes (RZCl and RECl with lithium gives reduction products in addition to the organolithium compound. This reduction occurs with partial inversion of the double bond while retention of configuration takes place when the n-butyllithium exchange reaction is used.A partial inversion also occurs when Z- and E-4-bromohept-3-enes (RZBr and REBr) are formed from exchange with the corresponding vinylic organolithium and dibromoethane.A vinylic radical is postulated to explain the lack of stereospecificity during the formation of the Li bond in the reaction with lithium. 相似文献
The method for preparation of ethyl α-nitrocinnamates by nitroacetic acid ester alkenylation with aromatic aldehydes in the presence of acetic acid and β-alanine has been modified. Structures of the prepared compounds have been proved by electronic, IR, 1H, and 13C-{1H} NMR spectroscopy (including heteronuclear correlation experiments 1H-13C HMQC and 1H-13C HMBC). In solution these compounds exist in the form of Z-isomer; the Z?E isomerization is observed in the case of the compound containing strong electron-donor group [N(CH3)2] at benzene ring. 相似文献
The structure of the carbanionic species 4 formed from diethyl(2-oxopropyl)phosphonate and t-BuOK has been studied by 1H, 13C and 31P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4Z (C) is observed. Two slowly interconverting species 4Z and 4E co-exist when the anion-cation interaction is loose, i.e. in Me2SO and when the gegenion K+ is complexed to (2,2,2)cryptand in Me2SO. The anionic carbon of 4Z and 4E is planar, and they have a strong enolate character as shown by the barrier to rotation around the C-1? C-2 bond (ΔGc?~92 KJ mol?1). Their structures are compared to those of the related E and Z 1-diethylphosphonato-2-trimethylsilyloxypropenes and to (acetylmethylene)triphenylphosphorane. 相似文献
The scattering of slow electrons and positrons by lithium metal dimer has been studied in the laboratory frame close coupling method. The effect of polarization is included through the parameter free model correlation potential given by Perdew and Zunger. In the case of electron, the exchange kernel is replaced by a local model exchange potential as used by Sur and Ghosh. To have a convergent result seven rotational states (j=0, 2, 4, 6, 8, 10, 12) are retained in the coupling scheme. The results for elastic, rotational and total cross sections fore? — Li2 ande+ — Li2 are reported. The electron results are in fair agreement with measured values and existing theoretical predictions. 相似文献
The Kais function is an exact solution of the Schrödinger equation for a pair of electrons trapped in a parabolic potential well with r12?1 electron-electron interaction. Partial wave analysis (PWA) of the Kais function yields EL = E + C1(L + \-C?12)?3 + O(L?5) where E is the exact energy and EL the energy of a renormalized finite sum of partial waves omitting all waves with angular momentum ? > L. Slight rearrangement of an earlier result by Hill shows that the corresponding full CI energy differs from EL only by terms of order O(L?5) with FCI values of C1 and \-C?12 identical to PWA values. The dimensionless \-C2 parameter is weakly dependent upon the size of the physical system. Its value is 0.788 for the Kais function, and 0.893 for the less diffuse helium atom, and approaches \-C2→ 1 in the limit of an infinitely compact charge distribution. The ?th energy increment satisfies an approximate virial theorem which becomes exact in the high ? limit. This analysis, formulated to facilitate use of the Maple system for symbolic computing, lays the mathematical ground work for subsequent studies of the electron correlation cusp problem. The direction of future papers in this series is outlined. 相似文献
Formation and protonation of aromatic anion radicals in 2-propanol were studied by kinetic spectrophotometric pulse radiolysis. All polycyclic hydrocarbons studied were found to react very rapidly with e?solv. Those with relatively high electron affinity were also reduced by (CH3)2CO?. The anion radicals formed undergo protonation by direct reaction with the alcohol molecule. The rate constants for this protonation vary from ≈ 6 × 105 s?1 for cis-stilbene and naphthalene down to 20 s?1 for perylene. The variations in rates are discussed in terms of changes in singlet energy separation (ΔES1 ← S0). The logarithm of the protonation rate constant for alternant hydrocarbons is linearly dependent on ΔES1 ← S0. 相似文献
A straightforward method to prepare symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes is described. High E/Z ratio 1-bromo-1-fluoroalkenes, prepared by isomerization from the E/Z ≈ 1:1 isomeric mixtures, reacted with Bu3SnSnBu3 and Pd(PPh3)4 to afford (1Z, 3Z)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in good yield. (Z)-1-Bromo-1-fluoroalkenes, which were prepared by kinetic reduction from 1-bromo-1-fluoroalkenes (E/Z ≈ 1:1), can undergo similar reaction with Bu3SnSnBu3 and Pd(PPh3)4/CuI to prepare (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes. 相似文献
The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λmax = 363 nm, E = 1.69 × 104liters · mol?1cm?1), pi-colinadehyde (λmax = 363 nm, E = 2.38 × 104liters · mol?1cm?1), 6-methyl-picolinaldehyde (λmax = 363 nm, E = 2.28 × 104liters · mol?1cm?1), di-2-pyridylketone (λmax = 380 nm, E = 2.08 × 104liters · mol?1cm?1), and o-naphthoquinone (λmax = 540 nm, E = 1.03 × 104liters · mol?1cm?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λmax = 430 nm, E = 2.56 × 104liters · mol?1cm?1) and dipyridylglyoxal (λmax = 363 nm, E = 2.37 × 104liters · mol?1cm?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given. 相似文献
The activation mechanism of the nitrous oxide (N2O) with the Ta(NH2)3 complex on the singlet and triplet potential energy surfaces has been investigated using the hybrid exchange correlation functional B3LYP. The minimum energy crossing point (MECP) is located by using the methods of Harvey et al. The rate-determining step of the N–O activation reaction is the intersystem crossing from 12 to 32. The reacting system will change its spin multiplicities from the singlet state to the triplet state near MECP-1, which takes place with a spin crossing barrier of 32.5 kcal mol?1, and then move on the triplet potential energy surface as the reaction proceeds. Analysis of spin–orbit coupling (SOC) using localized orbitals shows that MECP-1 will produce the significant SOC matrix element, the value of SOC is 272.46 cm?1, due to the electron shift between two perpendicular π orbitals with the same rotation direction and the contribution from heavy atom Ta. The rate coefficients are calculated using Non-adiabatic Rice-Ramsperger-Kassel-Marcus (RRKM). Results indicate that the coefficients, k(E), are exceedingly high, k(E) > 1012 s?1, for energies above the intersystem crossing barrier (32.5 kcal mol?1); however, in the lower temperature range of 200–600 K, the intersystem crossing is very slow, k(T) < 10?6 s?1. 相似文献
The correlation energy (Ecorr) is found to be inversely proportional to the product of the electron pair size (2>) and the square of the effective nuclear charge (Zeff) for the helium-like ions. 相似文献
In a molecular beam the effects of vibrational pumping of SF6 (ν3 = 948 cm?1) are studied, using a line-tunable cw CO2 laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (xE/D ≤ 1), a thermal redistribution of the ν3 excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm?1. For excitation in the relatively rare collision regime (xE/D ? 4), a structured non-thermal ν1 Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν3 mode. The value of Trot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν3(948 cm?1)+ΔErot → h(ν4 + ν6)(962 cm?1) relative to the near-resonant transfer rate (hν3 + hν3 → 2hν3 + 3.5 cm?1)]. 相似文献
Three thiophene‐S,S‐dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm2 V?1 s?1), despite its rather disordered chain packing. 相似文献
2-Anthrylethylene derivatives 1E?C5E and 1Z are synthesized to study the cis-trans photoisomerization. Interestingly, unlike 9-anthrylethylene derivatives, 2-anthrylethylene derivatives 1E to 5E do not exhibit E(trans) to Z (cis) photoisomerization upon direct and triplet sensitization. One-way Z (cis) to E (trans) photoisomerization of 1Z is found to be very efficient under direct and triplet sensitization conditions, demonstrating the involvement of both singlet and triplet states. 1E?C5E exhibits excitation wavelength dependent fluorescence indicating the existence of conformers (rotamers) at room temperature, which is confirmed by fluorescence lifetimes measurements of compounds 1E and 2E. Theoretical studies are carried out at DFT and ab initio methodology and the calculated relative energy difference of the conformers is very small; it ranges between 2.9 kJ·mol?1 to 6.3 kJ·mol?1 for both ground and excited states. 相似文献
The development of storage rings and electromagnetic traps for heavy charged particles is opening up new regimes of atomic physics, including, in particular, spectroscopic studies of Rydberg helium-like ions — with nuclear chargeZ, one electron in the 1s state, and one electron in a near-hydrogenic state of highn andl <n, withn andl the principal and orbital quantum numbers, respectively. We consider the possibility of detecting energy shifts due to retardation, ΔEret (n,l), Casimir-like effects. These are quantum electrodynamic (QED) retardation effects associated with the finite speed of light. (As opposed to basically kinematic and dynamic QED effects for small quantum numbersn andl, the appropriate expansion parameter forn andl large for retardation QED corrections is notZ(e2/?c) but [(Z ? 1)/n2Z2](?c/e2).) We wish to provide some orientation to those planning experiments in the area, with regard to the choices ofn,l, andZ most likely to be able to generate a high-precision confirmation of a retarded interaction. To do so, we provide extensive tables of estimates, for 1s,nl states, of ΔEret(n,l), of radiative widths, and ofE, the spin-independent (“electric” fine structure) energy in the absence of retardation shifts, for (nuclear spin zero) ions withZ=2, 6, 8, 16 and 20. These ions might be experimentally accessible in storage rings, and theZ's are low enough that virtual pair production effects may not yet be significant. There is also a brief survey of possible experimental techniques. 相似文献