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1.
Closo-B nH n−2(CO) 2 ( n = 5–12), isolobal analogues of closo-C 2B n−2H n, have been investigated at the B3LYP/6-311+G **density functional level of theory. The most stable isomers of closo-B nH n−2(CO) 2 are similar to those of closo-C 2B n−2H n in geometric patterns apart from closo-B 6H 4(CO) 2, and closo-B nH n−2(CO) 2 is much less strained than closo-C 2B n−2H n. Energetic analysis identifies closo-B 6H 4(CO) 2, closo-B 12H 10(CO) 2 and closo-B 10H 8(CO) 2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B nH n−2(CO) 2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed. 相似文献
3.
The structures of alkali halide clusters Na nF n, Li nF n and Na nCl n, and their metal-excess clusters Na nF n−1+, Li nF n−1+ and Na nCl n−1+ were investigated by the ab initio molecular orbital method for cluster sizes from 1 to 14. The magic numbers for the neutral clusters Na nF n, Li nF n and Na nCl n are 4, 6, and 8. The most stable structure for these cluster sizes is a perfect crystallite for Na nF n and Na nCl n, and a double ring for Li nF n. The magic numbers for the metal-excess clusters are 5 and 8, which are near ideal cuboids with (100) facets. 相似文献
4.
Abstract— The rapid bimolecular reaction SO + O 3= SO 2+O 2+ 106 kcal/mole yields electronically excited SO 2 in the 3B 1 and 1B 2 states with some vibrational excitation, as well as SO 2 in its electronic ground state. It is shown that k 1 = 1.5 x 10 12 exp (-2100/ RT ) cm 2 mole -1 s- 1 and that the formation of electronically excited SO 2 involves higher activation energies. 相似文献
6.
硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。 相似文献
7.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
11.
The syntheses of the 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′ 3tach)Cl 2] (M = Ti or Zr (NMR only); R = Bu t or 2,6-C 6H 3Pr i2; R′ = Me or Bu t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu t)(Me 3tach)(CH 2Ph) 2]. The tert-butylimido ligand in [Ti(NBu t)(Me 3tach)Cl 2] undergoes exchange with ArNH 2 (Ar = 4-C 6H 4Me or 2,6-C 6H 4Me or 2,6-C 6H 3Pr i2) to form the corresponding arylimides [Ti(NAr)(Me 3tach)Cl 2]. The Me 3tach ring in [Ti(NR)(Me 3tach)Cl 2] undergoes slow exchange with Bu t3tach or Me 3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu t3tach)Cl 2] and [Ti(NR)(Me 3tacn)Cl 2], respectively. The complexes [Ti(NR)(Me 3tach)X 2] (R = Bu t or 2,6-C 6H 3Pr i2; X = Cl or CH 2Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me 3tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu t3tach)Cl 2] (R = Bu t or 2,6-C 6H 3Pr i2) and [Ti(NBu t)(Me 3tach)(X) 2] [X= Cl or CH 2Ph) are reported. Me 3tach and Bu t3tach = 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane, respectively. 相似文献
14.
Zeeman spectral data are presented for the 2Π 3/2: J = 7/2 → J= 9/2, 2Π 3/2: J= 7/2→ 2Π 1/2: J= 5/2 and 2Π 3/2 J= 3/2→ J = 5/2 transitions in OD. Data for the 2Π 3/2. J=3/2→ J= 5/2 and 2Π 3/2 J= 5/2 → 2Π l/2 : J= 3/2 transitions in OH, taken under similar conditions, are included. 相似文献
17.
The thermodynamic data (Δ G0, Δ H0 and TΔ S0) of the solvation of tetraphenylarsonium-tetraphenylborate (Ph 4AsPh 4B) and its neutral parts, tetraphenylgermanium (Ph 4Ge) and tetraphenylmethane (Ph 4C) in methanol— N,N-dimethylformamide mixed solvents are discussed. The values of the free energy of transfer, ΔsMG0, are calculated from measurements of the solubilities of Ph4AsPh4B, Ph4Ge and Ph4C in the successive fractions of MeOH in DMF at three different temperatures (15, 25, 35°C). The values of ΔsMH0 and TΔsMS0 for the derivatives are calculated from ΔsMG0 values. The values of ΔsMG0, ΔsMH0 and TΔsMS0 of tetraphenylarsonium and tetraphenylborate ions have also been carefully calculated. The ratios of ΔsMG0 values (ΔsMG0 = ΔG0(+)/ΔG0(−)) were found to be greater than unity. Similarly, the ratios of ΔsMH0 and TΔsMS0 for the positive and negative ions were found to be greater than unity. 相似文献
18.
Abstract The crystalline phosphoranes have been obtained. IR-, UV- and NMR spectra of phosphoranes (Ia,b) and their interaction products with nitrogen bases have been investigated. It was determined that phosphoranes have structure (I) with pentacoordinate phosphorus and phenolic hydroxy group, while their products of interactions with nitrogen bases have the ionic structure (II) with hexacoordinate phosphorus (II). The X-ray difraction approves the structure (I) for phosphorane Ib. 相似文献
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