固体高辨核磁共振技术对改性金属离子在HZSM-5分子筛中的行为研究

使用固体高分辨核样共振技术研究Zn^2+, Ga^3+,等离子在HZSM-5分子筛中的行为。结果表明, Ga^3+离子主要定位于HZSM-5外表面, 不能抑制骨架脱铝; Zn^2+离子进入了HZSM-5内孔道, 取代了桥羟基上部分质子位, 能稳定沸石骨架。Ga^3+,Zn^2+离子均未进入沸石骨架位。骨架脱铝顺序为: GaHZSM-5>ZnHZSM-5》BaHZSM-5≌CaHZSM-5。     

XeCl准分子激光引发香芹酮的化学反应

本文报道了用XeCl准分子激光引发香芹酮(1)化学反应的研究结果.根据反应产物香芹酮樟脑(2)和1-挂,5-二甲基-顺2-[(乙氧羰基)甲基]双环[2.1.1]己烷(3)与激光照射能量的关系,得出香芹酮的1→2→3的反应过程.实验表明,在低激光强度照射时,每照射1焦耳能量生成2和3的量随着激光强度的增加而增加,并显示出饱和趋势.同时在照射过程中观察到浓度效应和发光.     

Interpretation of XENON1T excess with MeV boosted dark matter

The XENON1T excess of keV electron recoil events may be induced by the scattering of electrons and long-lived particles with an MeV mass and high speed. We consider a tangible model composed of two scalar MeV dark matter (DM) particles, \begin{document}$ S_A $\end{document} and \begin{document}$ S_B $\end{document}, to interpret the XENON1T keV excess via boosted \begin{document}$ S_B $\end{document}. A small mass splitting \begin{document}$ m_{S_A}-m_{S_B}>0 $\end{document} is introduced, and the boosted \begin{document}$ S_B $\end{document} can be produced using the dark annihilation process of \begin{document}$ S_A S_A^\dagger \to \phi \to S_B S_B^\dagger $\end{document} via a resonant scalar ?. \begin{document}$ S_B- $\end{document}electron scattering is intermediated by a vector boson X. Although the constraints from Big Bang nucleosynthesis, cosmic microwave background (CMB), and low-energy experiments set the \begin{document}$ X- $\end{document}mediated \begin{document}$ S_B- $\end{document}electron scattering cross section to be \begin{document}$ \lesssim 10^{-35} \mathrm{cm}^2 $\end{document}, the MeV scale DM with a resonance enhanced dark annihilation today can still provide sufficient boosted \begin{document}$ S_B $\end{document} and induce the XENON1T keV excess. The relic density of \begin{document}$ S_B $\end{document} is significantly reduced by the s-wave process \begin{document}$ S_B S_B^\dagger \to X X $\end{document}, which is permitted by the constraints from CMB and 21-cm absorption. A very small relic fraction of \begin{document}$ S_B $\end{document} is compatible with the stringent bounds on un-boosted \begin{document}$ S_B $\end{document}-electron scattering in DM direct detection, and the \begin{document}$ S_A $\end{document}-electron scattering is also allowed.