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41.
Detailed analysis of the vibronic structure in the electronic absorption spectrum of Cs2NaYbF6 at temperatures between 10 and 300 K enables the crystal field energy level diagram of Yb3+ in this cubic host to be deduced. Ultraviolet and visible laser excitation of Cs2NaYbF6, Cs2NaY(0.9)Yb(0.1)F6, and Cs2NaHo(0.99)Yb(0.01)F6 give spectral features mainly due to Yb3+ being situated at a range of defect sites. The 4f13 crystal field analyses of octahedral YbX6(3-) (X = F, Cl, Br) systems show the expected trends in parameter values, but the energy level fits are poor. Inclusion of the interaction with the charge-transfer configuration 4f14np5 provides an exact fitting of energy levels for YbX6(3-), and a smooth variation of ff and fp crystal field parameters for Cs2NaLnCl6 (Ln = Er, Tm, Yb) is observed. 相似文献
42.
The recent measurement of negative higher-order Kerr effect (HOKE) terms in gases has given rise to a controversial debate, fed by its impact on short laser pulse propagation. By comparing the experimentally measured yield of the third and fifth harmonics, with both an analytical and a full comprehensive numerical propagation model, we confirm the absolute and relative values of the reported HOKE indices. 相似文献
43.
We report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to postpulse alignment, as well as to the free electron density induced by the ultrashort laser pulse. The analysis of the resulting signal thus gives access to absolute single-ionization probabilities calibrated through the degree of alignment, provided that free electrons are produced mainly by single ionization. The relevance of the method is assessed in N2. 相似文献
44.
Control of the third-harmonic generation process through an external electromagnetic field is observed in atomic Ca. The conversion efficiency can be modified when the third harmonic is produced in the vicinity of an autoionizing state. A second laser is used to produce strong radiative coupling between a low-lying bound state and the autoionizing state. 相似文献
45.
We show that two overlapping linearly polarized laser pulses of frequencies omega and its second harmonic 2omega can strongly orient linear polar molecules, by adiabatic passage along dressed states. The resulting robust orientation can be interpreted as a laser-induced localization in the effective double well potential created by the fields, which induces a preliminary molecular alignment. The direction of the orientation can be selected by the relative phase of the fields. 相似文献
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48.
Allen BD Cintrat JC Faucher N Berthault P Rousseau B O'Leary DJ 《Journal of the American Chemical Society》2005,127(1):412-420
(N-CHDT)-(alpha)-isosparteinium ditosylamide can be used in conjunction with tritium NMR spectroscopy to assign the configuration of an intact stereogenic (chiral) methyl group. The S-CHDT group has a (3)H chemical shift that is 49 ppb downfield of the R-CHDT resonance. The sign and magnitude of this chemical shift difference of these diastereotopic tritium nuclei are found to be in agreement with predictions made via a purely ab initio computational approach. The chemical shift difference is due to an equilibrium isotope effect originating from a novel CH(3)(...)N hydrogen bond. Despite the improved tritium chemical shift dispersion, this method is not useful for determining the enantiopurity of CHDTN(Tos)(2) due to partial racemization that occurs during the derivatization step. Milder methylation conditions are described for reactions using methyl p-toluenesulfonate or methyl-d(3) triflate. These studies suggest that (-)-(alpha)-isosparteine is a potential new reagent for chirality analysis of methyl groups originating from suitably reactive electrophiles. 相似文献
49.
We show that a linear molecule subjected to a short specific elliptically polarized laser field yields post-pulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high alignments along both directions are derived. 相似文献
50.
The field-free alignment of CO2 produced in response to the excitation of a molecule by a high-intensity femtosecond pump pulse is measured with a simple coronography-like technique. The technique is based on the defocusing of a time-delayed probe pulse produced by the spatial distribution of aligned molecules. In the intensity regime explored here, the technique is shown to give valuable information about dynamic alignment. With the help of simulations, the degree of alignment is extracted from the data. 相似文献