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81.
Porphycene, an isomer that can replace porphin in chemical and biochemical contexts, is predicted by ab initio calculation to exhibit a global diatropic pi ring current with bifurcation across the four pyrrole units of the macrocycle. Analysis of the orbital contributions to the current density in porphycene reveals that the global current, with its bifurcation feature, is attributable to the four electrons of the near-degenerate HOMO levels, the same set of active electrons that feature in the well-known four-orbital model of the electronic spectra of porphyrins. Integration of the current density gives 1H, 13C and 15N NMR shieldings that are compatible with the observed low-field shifts of peripheral and bridge protons and high-field shift of the internal NH protons, assignment of the 13C NMR spectrum and the single average 15N chemical shift resulting from rapid NH tautomerism. Geometries were calculated with the DFT B3LYP functional, the current density maps were calculated with the ipsocentric coupled-Hartree-Fock CTOCD-DZ method, and the shieldings with the CTOCD-PZ2 variant, all in the same 6-31G** basis. 相似文献
82.
Using a multistep state-selective excitation scheme, fluorescence-dip spectra of carbon monoxide have been recorded in the energy region between 106 100 and 112 200 cm(-1). Prominent groups of bands were tentatively identified as transitions into the 6f em leader10f (v=0) and 9psigma em leader11psigma (v=0) triplet Rydberg series. For the f complex states, molecular constants have been calculated. The triplet f levels show an unusually large rotational constant and are located at higher energies than their singlet counterparts. Copyright 2001 Academic Press. 相似文献
83.
Advances in Computational Mathematics - 相似文献
84.
The through space NMR shieldings (TSNMRS) of dodecahedrane C20H20, of the isomeric hydrocarbons C20H12, of the ions C20H122+ and C20H122?, of the fluxional fullerene C20 and of its dication C202+ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G1 geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved π-conjugation in the compounds studied could be quantified. 相似文献
85.
86.
Peter Schiller Hans-Jörg Mögel Erich Miersemann 《Journal of Mathematical Fluid Mechanics》2010,12(2):293-305
For a class of disjoining pressure potentials the existence of stable liquid layers on solid surfaces is studied. In some
cases of solid configurations with simple geometries explicit results are obtained, in particular for a single cylindrical
or spherical cavity. No smallness for the thickness of the layer is assumed. 相似文献
87.
88.
Erich P. Ippen 《Hyperfine Interactions》1987,37(1-4):163-184
The first section will discuss the generation of picosecond and femtosecond laser pulses, their propagation and compression
in optical fibers, and their amplification for nonlinear spectroscopic applications. Laser systems for different wavelength
regimes and pulse measurement techniques will be described.
The second section will extend the discussion of picosecond and femtosecond measurement to studies of ultrafast processes
in materials. Pump-probe and transient four-wave-mixing methods will be analyzed. Examples of application to both molecular
and solid state systems will be presented. 相似文献
89.
90.