不同取代基对喹啉电子光谱影响的理论研究

不同取代基团会引起电子光谱发生不同的变化,为获得分子结构与电子光谱之间的关系,采用量子化学计算方法进行了理论分析。使用DFT、CIS分别对基态、激发态进行几何结构优化,再用TDDFT计算优化结果得出电子光谱。结果表明:不同取代基团都改变了碳氮环基态、激发态的几何构型,前线区域轨道能量,π电子共轭系统,这些变化都导致电子光谱发生相应变化。得出不同取代基对电子光谱的影响规律,为电子光谱分析鉴定衍生物提供了理论参考。     

The influence of char surface oxidation on thermal annealing and loss of combustion reactivity

Thermal annealing associated with heat treatment of coal chars affects gasification reactivity and levels of unburned carbon in residual ash from coal-fired furnaces. The present study addresses the effect of char surface oxidation, occurring upon exposure to oxygen, on the course of thermal annealing, and related loss of combustion reactivity. This goal is pursued by comparing the extent of thermal annealing suffered by coal char upon heat treatment in a nitrogen atmosphere with that of chars that underwent oxidation prior to or during heat treatment. Oxidation of char was accomplished by supplying single or multiple pulses of air during the heat treatment, which were sufficient to oxidize the char surface but small enough to limit carbon gasification to less than 5%. The extent of thermal annealing was characterized both in terms of the loss of combustion reactivity and of the development of structural anisotropy of char samples, investigated by HRTEM. Results of the present study confirm that heat treatment reduces oxyreactivity of char samples, the effect being more pronounced at temperatures exceeding 1200 °C. Oxidation of samples mitigates the effects of heat treatment, as demonstrated by the smaller loss of gasification reactivity and by the more limited development of structural anisotropy of oxidized samples. Correspondingly, elemental analysis of samples indicates the formation of stable surface oxides upon oxidation, that are subsequently desorbed upon heat treatment. At temperatures exceeding 1200 °C, the effect of oxidation vanishes. Results are analysed and discussed in the light of the possible hindrance of thermal annealing due to the formation of stable surface oxides and of the parallel modifications occurring to the ash constituents.     

The influence of deformation on the reactivity of C=C bonds in reactions with ozone

The influence of strain in the reaction center containing a double bond on double bond reactivity at the first stage of the reaction with ozone was studied by the B3LYP density functional theory method and ab initio MP2, CCSD, QCISD, and MRMP2 multireference methods. The 6-31+G** and 6-311+G** basis sets were used. The reactions of ozone with ethylene and butylene were studied. Deformation (ɛ) was introduced by using the C=C bond length or the distance between extreme carbon atoms as a coordinate not subjected to optimization. Stretching of the double bond was found to activate the reaction by the mechanisms of symmetrical and nonsymmetrical addition. The sensitivities to deformation were similar in the two channels. When the butene fragment as a whole was stretched, a different picture was observed, and the reaction with ozone was decelerated. In both cases, the logarithms of rate constants linearly depended on ɛ. The calculation results were analyzed using the approach developed earlier, which allowed the calculation results to be used to obtain an analytic form of the dependence of activation energy E _a on the strength of bonds and to relate deformation-induced changes in E _a to the length and rigidity of the initial and transition states.     

Intramolecular cyclization of 1-(2-arylethyl)tetrahydro-6-hydroxy-1H-pyrimidin-2-thiones: effect of substituents on reactivity

Convenient synthetic procedures for 1,2,3,6,7, 11b-hexahydro-4H-pyrimido[6, 1 -a] isoquinolin-4-thiones and 2,3,6,7,12,12b-hexahydro-1H-pyrimido[1′,6′:1,2]pyrido[3,4-b]indole-4-thiones have been developed. Structural factors which influence on a cascade cyclization process have been elucidated.     

Effect of substituents and protonation on photolysis of the 2,5-diphenyl-oxazole molecule

Based on quantum chemical calculations, we consider the effect of substitution by groups with different donor-acceptor properties and protonation on the probability of opening of the oxazole ring of the 2,5-diphenyloxazole molecule (PPO). We show the determining role of the hydrogen-containing medium in this photoconversion. We have established that a substituent introduced into the para position of the 5-phenyl radical, depending on its donor-acceptor properties, can either enhance the efficiency of photolysis (donor substituent) or weaken it (acceptor substituent). We have found the photodissociative states and have determined their multiplicity for the considered substituted PPOs. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 84–90, July 1997.     

Effect of metal and substituents on the quasi-line spectra of some metalloporphyrins

Absorption spectra are reported for a number of metalloporphyrins in n-octane. For ZnP and PdP, sharp quasi-lines with linewidths ≈4 cm^?1 are observed at 15 and 35 K, respectively. The narrowest linewidths for PtP are ≈12 cm at 15 K, while NiP and CuP show no quasi-linear structure. In these latter cases, quasi-linewidth is attributed to electronic radiationless decay of the visible excited state. The various vibronic bands within Q(1, 0) are tabulated. The quasi-line structures for several zinc porphyrins at 77 K are also reported. Generally, these are not as sharp as those found in ZnP; in particular, Zn tetraphenyl porphin shows no quasi-linear structure. In these cases, the quasi-line structure is attributed to inhomogeneous broadening.     

On the influence of hydrogen on the low-temperature reactivity of n-pentane, 1-pentene and 3-pentanone: an experimental and modeling study

Hydrogen can be blended with other surrogate fuels to avoid its hazard as a highly flammable and explosive gas. The effect of hydrogen addition on the ignition delay times of n-pentane, 3-pentanone, and 1-pentene was investigated by measuring the ignition delay times in a rapid compression machine. The experiments were performed at pressures of 10, 15, and 20 bar, equivalence ratios 0.5 and 1 and for temperatures ranging from 650 to 970 K. The molar ratios of hydrogen in the fuel mixtures were 0, 25 and 50%. The experimental data were simulated using recent models from literature, yielding good agreement. The overall observations conclude to a minor effect of hydrogen addition in the case of n-pentane and 3-pentanone, resulting in a decrease of the reactivity when the mole fraction of hydrogen increases. Hydrogen does however not impact the ignition delay times of 1-pentene significantly. Kinetic analysis is performed to shed light into the processes responsible for this phenomenon.     

Influence of substituents on the structure of dimers of copper porphyrins

Journal of Applied Spectroscopy -     

The reactivity and auger chemical shift of oxygen adsorbed on platinum

The reaction of carbon monoxide with oxygen chemisorbcd on polycrystalline platinum has been studied using Auger spectroscopy. Two types of chemisorbed oxygen are distinguished on the basis of Auger electron chemical shifts and reactivity towards carbon monoxide. When the substrate is below 800 K, a single very reactive type of chemisorbed oxygen is formed. Above 800 K a new species begins to form which is characterized by an Auger chemical shift of about 6 eV and by low reactivity. The decay of the oxygen Auger signal using several fixed pressures of carbon monoxide was measured. The reaction is first order in carbon monoxide pressure but no clear decision can be made about the order with respect to oxygen coverage. With the reaction $\text{CO +}\text{1}\text{20}{}_2\text{→ CO}{}_2$ operating at steady-state, the oxygen coverage was measured as a function of CO pressure. In the region 363–600 K, the steady state oxygen coverage began to decline measurably when reached 0.1. When p_CO>p_O2the oxygen coverage became immeasurably small. A simple model is used to relate these phenomena to observed carbon dioxide production rates.     

The influence of noise on the logistic model

The behavior of the logistic system which is generated by the functionf(x =ax (1–x) changes in an interesting way if it is perturbed by external noise. It turns out that the chaotic behavior which was predicted by Li and Yorke for orbits of period 3, becomes visible and that a sequence of mergence transitions occurs at the critical parameter. The change of the invariant probability density and the Lyapunov exponents are examined numerically. The power spectrum for the period 3 orbit for different fluctuations is calculated and a recursion formula for the time evolution of the probability density is presented as a discrete-time analog of a Chapman-Kolmogorov equation.     

The influence of doping on the laser performance

We report a comparison, at low inversion population density, between two Yb:YAG ceramics lasers with different doping levels (10 and 20 at %) emitting at 1030 and 1050 nm. At the shorter lasing wavelength, the efficiency and the maximum output power of both samples are almost independent on the concentration of dopants. Conversely, at 1050 nm the two samples show a sizeable difference in the performances for higher values of the pump power. The results are compared with numerical simulations accounting for the pump beam and the laser radiation in order to map the temperature distribution experienced by the samples. We studied the effects of the reinjection of the pump inside the active medium. We obtained an output power of 10 W with a slope efficiency of 59% in respect of the pump power on the 20 at % sample. Finally, we report the tuning range for the heavier-doped sample (20 at %), which, to the best of our knowledge, is the first measurement on an heavily doped sample even reported in literature.