Terahertz spectroscopic investigations of caffeine and 3-acetylmorphine

Experimental and theoretical investigations of THz spectral features of caffeine and 3-acetylmorphine in the region of 0.2-2.6 THz have been presented. The refractive indices and absorption coefficients of the two drugs were obtained by a terahertz time-domain spectroscopy (THz-TDS) technique. The simulated absorption spectra using the density functional theory (DFT) and Hartree-Fork (HF) are in agreement with the experimental data. The observed spectral absorption features were assigned based on DFT and HF calculation.     

二氟甲烷分子3a1和2b2轨道的电子动量谱

借助电子动量谱学结合量子化学理论和其他方法可以给出轨道电子在整个空间的分布信息,由此给出电子运动的完备描述[1,2 ] .清华大学电子动量谱学实验室近几年已成功地对甲烷[3] 、异丁烷[4 ] 、环戊烷[5] 、二乙酰等[6 ] 分子的轨道电子动量分布进行了测量.我们利用第二代电子动量谱仪首次对CH2 F2 分子3a1和2b2 轨道的电子动量谱进行测量,并与理论计算结果作了比较.同时还计算了坐标空间和动量空间中电子在x - y平面的密度分布.电子动量谱学最基本的过程是(e ,2e)反应,即电子与靶粒子碰撞而发生的电离过程.而对于(e ,2e)反应,含有大量信…     

Influence of donor and acceptor groups on the S-T energy gap for thermally activated delayed fluorescence emitters

Molecules composed of different donors and acceptors are theoretically designed as potential thermally activated delayed fluorescence emitters, and their singlet–triplet (S-T) energy gap is studied using the optimal Hartree–Fork method. It is found that the S-T energy gap is in reverse proportional to the electron-donating ability. Stronger electron-donating ability of donors will induce smaller highest occupied molecular orbital–lowest unoccupied molecular orbital overlap and also a smaller S-T energy gap. Based on our calculation results, three molecules are proposed to have great potential to be used as thermally activated delayed fluorescence emitters in organic light-emitting diodes.     

双碳醇水溶液的1H NMR实验与理论分析

In this study, ¹H nuclear magnetic resonance (NMR) measurements and quantum chemistry (QC) studies of ethanol (ET)-water mixtures and ethylene glycol (EG)-water mixtures are carried out at different temperatures to discuss the interactions between water and the alcohols present in the mixtures. From ¹H NMR spectra, it is observed that the chemical shift of the water proton shows two different trends in the ET-water mixtures and the EG-water mixtures. With increasing water concentration, the water proton chemical shift decreases dramatically for ET-water mixtures, while the chemical shift increases slowly for EG-water mixtures. The alcohol hydroxyl proton resonance peaks of both ET and EG shift to lower field with decreasing water concentration. It is found that the resonance peaks of all alkyl protons shift monotonically to low field with increasing alcohol concentration at different temperatures. The geometry optimization results indicate the formation of H-bonds between the water molecules and the hydroxyl groups of the alcohols alongside the weakening of O-H bonds in the alcohols, which results in an O-H bond length decrease. It is interesting to note that the bond length values computed for C-C, C-H and O-H bond in both ET and EG are larger when calculated at the density functional theory (DFT) (B3LYP) level than when calculated using Hartree-Fock (HF) level of theory with the same polarization function and diffusion function. However, the O-H…O H-bond computed at HF level of theory is stronger than that calculated at DFT level of theory. The theoretical results are in good agreement with the experimental ones. In the calculation of NMR chemical shift, DFT(B3LYP) is better than HF, which implies that for the same method, the larger the basis sets are, the more accurate are the calculated values.     

二氟甲烷分子3a1和2b2轨道的电子动量谱

The electron momentum spectroscopy of the inner valence orbitals 3a1 and 2b2 of methylene fluoride was studied by electron momentum spectroscopy（EMS）. The experiment was performed using a high resolution（ΔE=1.15 eV FWHM,Δp=0. 1 a. u.）（e,2e）EMS spectrometer. The experimental momentum profiles of these two orbitals are compared with those calculated by Hartree-Fork method and Density Functional Theory.