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91.
In this paper we propose a method for carrying out variational transition state theory calculations without first obtaining
a converged minimum-energy path (MEP). We illustrate the method in two ways, first of all by employing an unconverged MEP
and secondly by using a dynamically optimized distinguished reaction path. Preliminary tests of the algorithm for the reactions
OH+H2→H2O+H and C2H5→C2H4+H are very encouraging.
Received: 22 January 1997 / Accepted: 11 March 1997 相似文献
92.
Stephen Cradock Donald C. McKean Moray W. MacKenzie 《Journal of Molecular Structure》1981,74(2):265-276
We have obtained microwave spectra of fully and partially deuterated germyl halides GeD3X and GeHD2X (X = F, Cl, Br, I) and analysed the infrared spectra in the GeH stretching region of the asymmetric species. The resulting Ao and Bo values have been combined with existing data on GeH3X to give improved structures for the germyl halides. The values of the HGeX angles obtained show a correlation with GeH stretching frequencies, as in methyl compounds, but there appears to be no such correlation between stretching frequencies and GeH bond lengths. 相似文献
93.
A Java applet that predicts solute losses during evaporation from a binary or ternary mixture has been developed which gives good agreement with experiment and can be used to estimate the boiling points of solutes, making use of information which is often collected and then discarded (http://www.ch.cam.ac.uk/magnus/rotavap/). 相似文献
94.
Najib Abusalbi David W. Schwenke C. Alden Mead Donald G. Truhlar 《Theoretical chemistry accounts》1987,71(5):333-357
We discuss molecule-frame and laboratory-frame symmetry-adapted formalisms for electron scattering by a spherical top. The molecule-frame formalism is based on the fixed-nuclear-orientation approximation, both for electronically elastic scattering by a vibrationally rigid molecule and also for the more general case where electronic excitation and vibrational degrees of freedom are included. The laboratory-frame formalism is based on the exact symmetries of the problem, which are carefully related to the approximate symmetries of the molecule-frame treatment. We present both the forward and backward transformations between the two representations. 相似文献
95.
We have performed large-scale close coupling calculations of rotational-to-rotational energy transfer in HF? HF collisions for the realistic potential energy surface of Brobjer and Murrell. We employ up to 525 angular terms in the expansion of the potential and up to 440 coupled channels in the rotational-orbital basis set. The results for zero total angular momentum are well converged for relative translational energies up to over 0.6 eV, and they show extensive rotational excitation. 相似文献
96.
The hydrolysis of chromate ion was studied potentiometrically in a concentration cell fitted with hydrogen electrodes by titrating basic NaCl–Na2CrO4 solutions with standardized HCl against a NaOH reference solution. The temperature was varied from 25 to 175°C at 25° intervals at the following ionic strengths (I): 0.1140, 0.2346, 0.5337, 0.9988, 2.940, and 5.239 (NaCl). Depending on the ionic strength, the molality of total chromium was varied from 0.001 to 0.100. The resulting titration curves could be resolved best in terms of three equilibria involving the formation of HCrO
4
–
(aq), Cr2O3– (aq), and CrO3Cl– (aq). The equilibrium quotients for all three reactions were fitted as a function of temperature and ionic strength, and the molal thermodynamic parameters that were computed from these relationships are tabulated at specific ionic strengths over the experimental temperature range. 相似文献
97.
It has been known for some time that the pre-treatment of platinum electrodes often effects subsequent electrochemical reactions. Part of the effect of pre-treatment is due to the fact that anodized or chemically oxidized platinum electrodes become coated to some degree with a film of platinum oxide. This work was concerned with quantitative measurement of kinetic parameters as a function of the extent of oxide film formation. Whenever possible, variations in reaction mechanisms are proposed.
Most of the experimental evidence has been taken from current-potential curves but the techniques of chronopotentiometry and microscopy were also used.
The reduction of vanadiumV chromiumVI, arsenicV, iodate and oxygen were investigated as well as the oxidation of vanadiumIV, arsenicIII, oxalic acid, and formic acid. The presence of the platinum oxide film effected the reactions studied in a variety of ways but in every case some variation in the kinetic parameters of the reactions studied was recorded. For a number of cases, a modified oxygen bridge theory was found useful. 相似文献
98.
DeClue MS Baldridge KK Künzler DE Kast P Hilvert D 《Journal of the American Chemical Society》2005,127(43):15002-15003
Isochorismate pyruvate lyase (IPL) catalyzes the cleavage of isochorismate to give salicylate and pyruvate, a key step in bacterial siderophore biosynthesis. We investigated the enzyme from Pseudomonas aeruginosa using isochorismate selectively deuterated at C2 as a substrate. Monitoring the reaction by 2H NMR spectroscopy revealed that the label is quantitatively transferred from C2 to C9, producing stoichiometric amounts of [3-2H]pyruvate as product. Moreover, the deuterium kinetic isotope effect of 2.34 +/- 0.08 on kcat indicates that C-H cleavage is significantly rate limiting. Consistent with these data, hybrid density functional theory (HDFT) calculations at the Becke3LYP/DZ+(2d,p) level of theory predict a concerted but highly asynchronous pericyclic transition structure, in which carbon-oxygen bond cleavage is more advanced than hydrogen atom transfer from C2 to C9; the calculated 2H isotope effect of 2.22 at C2 is in excellent accord with the experimental value. Together, these findings indicate that IPL should be added to the small set of proteins that are known to catalyze pericyclic reactions. They also raise the possibility that enzymes, such as chorismate pyruvate lyase, salicylate synthase, 4-amino-4-deoxychorismate lyase, and anthranilate synthase, which accelerate formally similar reaction steps, may also exploit pericyclic mechanisms. 相似文献
99.
John J. Monaghan Michael Barber Robert S. Bordoli R. Donald Sedgwick Andrew N. Tyler 《Journal of mass spectrometry : JMS》1983,18(2):75-82
Fast atom bombardment mass spectra of a range of involatile monophosphonated and mixed sulphonated/monophosphonated azo dyestuffs are presented. Good spectra are obtained and the fragmentations are discussed with special reference to the ions formed by cleavage of the azo linkage. The negative ion spectra are shown to be superior in terms of signal to background and structural information to those obtained in the positive ion mode. The results are compared with those obtained from sulphonated azo dyestuffs. 相似文献
100.
The CD spectra of L-2-methylpyrrolidine, L-prolinol, and their N-methylated derivatives have been determined. As in the 2-substituted piperidines, N-methylation results in an inversion of the sign of the Cotton effects (CE). However, the sign of the long-wavelength CE does not follow the simple helicity rule found for 2-substituted piperidines, since the pyrrolidine ring is itself chiral and makes its own contributions to the observed CE's. The rotational contribution due to pyrrolidine ring chirality appears to be opposite in sign to and larger in magnitude than that due to the 2-substituent in both the secondary and the tertiary amines. 相似文献