Pulsed photothermal phase-shift spectroscopy for weak absorption measurement

A novel photothermal phase-shift spectroscopy configuration based on the retro-reflected beam interference has been developed and its operational principle is described. The weak absorption measurement ability of this technique is experimentally proven with a water/ethanol solution of standard Pyronine G dye and the limit of detection is found to be 1.8 x 10(-6) absorbance. Potential applications of the technique are discussed.     

Angular distributions of photoelectrons in resonantly enhanced multiphoto ionization via the 7s[1 1/2]0 1 and 8s[1 1/2]0 1 states of Xe

Photoelectron angular distributions have been measured for the three-photon resonant one-photon ionization, (3+1), of Xe via the 7s[1 1/2]⁰ ₁ and 8s[1 1/2]⁰ ₁ states. The results are in good agreement with the theoretical predictions of Tang and Lambropoulos [13] for the 8s[1 1/2]⁰ ₁, but not for the 7s[1 1/2]⁰ ₁ state. Furthermore, the results are compared to those which have been obtained by Blazewicz et al. [1] for the three-photon resonant two-photon ionization, (3+2), of Xe via the 6s[1 1/2]⁰ ₁ state.     

Effect of substituents (NH2, OH, F) on structures and stability of lithofluorosilylenoids

Isomeric structures and energies of three kinds of lithofluorosilylenoids, R₂SiLiF (R = NH₂, OH, F) were studied using theab initio molecular orbital theory. The calculations show that thermal stability of the three-membered ring structures of these three kinds of silylenoids decreases in the order of substituents NH₂ > OH > F because of the conjugation between NH₂, OH or F and Si atom. The interaction of substituents R with Li atom makes R₂SiLiF have a structure with two Li-A-Si-F (A = N, O, F) four-membered rings, which is the most stable of the isomers of each of three kinds of silylenoids and whose stability decreases in the order of substituents F > OH > NH₂. Inductive effect of substituents influences the thermal stability of the linear structure of silylenoids.     

高效液相色谱手性流动相添加剂法拆分酪氨酸甲酯对映体

分别将β-环糊精、羟丙基-β-环糊精作为手性流动相添加剂，研究了酪氨酸甲酯对映体在反相HPLC系统中的拆分，考察了流动相种类、pH和手性流动相添加剂浓度对手性拆分的影响，建立了β-环糊精手性流动相添加剂法拆分酪氨酸甲酯对映体的方法。     

Structures, stabilities, and electronic and optical properties of c(58) fullerene isomers, ions, and metallofullerenes.

The 1205 classical isomers of fullerene C58, as well as one quasi-fullerene C58 isomer with a heptagonal ring (labeled as Cs:hept) have been investigated by the quantum chemical methods PM3, HCTH/3-21G, and B3LYP/6-31G(d). Isomer C3v:0001, which has the lowest number of adjacent pentagons, is predicted to be the most stable isomer, but the quasi-fullerene isomer Cs:hept is only 2.50 kcal mol-1 higher in energy. Systematic investigations of the electronic properties of C3v:0001 and Cs:hept find that the C3v:0001 isomer has high vertical electron affinity (3.19 eV). The nucleus-independent chemical shifts (NICS) value at the center of Cs:hept (-5.1 ppm) is more negative than that of C60 (-2.8 ppm). The NICS value at the center of the heptagonal ring in Cs:hept (-2.5 ppm) indicates weakly aromatic character. In contrast, the C58(6-) and C58(8-) ions of the C3v:0001 and Cs:hept geometries possess large aromatic character, with NICS values between -14.0 and -26.2 ppm. To clarify the thermodynamic stabilities of C58 isomers at different temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. The C3v:0001 isomer prevails in a wide range of temperatures, and the Cs:hept isomer is also an important component around 2800 K. The IR spectra of C58 isomers are simulated to facilitate experimental identification of different isomers. In addition, the electronic spectra and the second-order hyperpolarizabilities are predicted by ZINDO and the sum-over-states model. The static second-order hyperpolarizability of the C3v:0001 isomer is 96.5 % larger than that of C60, and its second-order hyperpolarizabilities at external field frequencies are at least nine times larger than those of C60.