一、引言
X射线单晶体衍射仪的英文名称是X-ray single cry stal diffractomet er,简写为XRD.
本仪器分析的对象是一粒单晶体,如一粒砂糖或一粒盐.在一粒单晶体中原子或原子团均是周期排列的.将X射线(如C u的Kα辐射)射到一粒单晶体上...一、引言
X射线单晶体衍射仪的英文名称是X-ray single cry stal diffractomet er,简写为XRD.
本仪器分析的对象是一粒单晶体,如一粒砂糖或一粒盐.在一粒单晶体中原子或原子团均是周期排列的.将X射线(如C u的Kα辐射)射到一粒单晶体上会发生衍射,由对衍射线的分析可以解析出原子在晶体中的排列规律,也即解出晶体的结构[1].物质或由其构成的材料的性能是与晶体的结构密切相关的,如金刚石和石墨都是由纯的碳构成的,由于它们的晶体结构不同就有着截然不同的性质.展开更多
X-ray diffraction （XRD） was used to study the structure of the organic crystallite unit （La, Lo doo2） in coals collected from Henan and Shanxi Provinces. XRD patterns of coal were collected in a step-scan mode （0...X-ray diffraction （XRD） was used to study the structure of the organic crystallite unit （La, Lo doo2） in coals collected from Henan and Shanxi Provinces. XRD patterns of coal were collected in a step-scan mode （0.1 °/step） over an angular range of 2-90° （20）, allowing 8 s at each step. The structure of the crystallite unit was determined from the Scherrer equation and peak parameters deduced from whole pattern fitting. The results show that the structure of the crystallite unit in coal is mainly controlled by the coal rank. As the coal rank increases the average diameter of a coal crystallite unit （La） increases, the interlayer spacing （doo2） decreases slightly, and the average height of a coal crystallite unit （Lc） increases at first but then decreases. A new diffraction peak from the crystallite unit in coal was found at a low scattering angle in the XRD pattern （2-10~）. This suggests a structure with an inter-layer spacing from 1.9 to 2.8 nm exists in coal crystallites.展开更多
A new sodium indium phosphate Na 6In 4[P 7O 24(OH) 5]·4H 2O was synthesized under a mild hydrothermal condition and its structure was determined by means of single-crystal X-ray diffraction methods. The title com...A new sodium indium phosphate Na 6In 4[P 7O 24(OH) 5]·4H 2O was synthesized under a mild hydrothermal condition and its structure was determined by means of single-crystal X-ray diffraction methods. The title compound crystallizes in a hexagonal system, space group P6 3, with a= 0.950 23(5) nm, b=0.950 23(5) nm, c=1.694 2(2) nm, α=90°, β=90°, γ=120°, V=1.324 8(2) nm 3, Z=8, structure refined to R=0.052 8 and wR=0.116 5 for 2 134 independent observed reflections. The three-dimensional network structure consists of helical chains formed by apex-sharing polyhedra. The connection of the chains results in 4- and 8-polyhedral rings and cages centered by three indium metal connecting oxygen atoms formed by three 4-rings. The three-connected oxygen atom is firstly observed in indium phosphate systems.展开更多
在宇宙开始大爆炸的时候,电荷变号与镜象反射共轭（CP）是对称的.但现在我们的宇宙绝大部分是正物质核子和电子等组成的,所以我们的宇宙是不对称的.D和L-丙氨酸通常称为对映体（enantiomer）,实际上它们并不是由正、反粒子组成的真正的...在宇宙开始大爆炸的时候,电荷变号与镜象反射共轭（CP）是对称的.但现在我们的宇宙绝大部分是正物质核子和电子等组成的,所以我们的宇宙是不对称的.D和L-丙氨酸通常称为对映体（enantiomer）,实际上它们并不是由正、反粒子组成的真正的对映体,而是空间反演的,即x--x,y--y,z--z的非对映异构体（diastereoisomer）,所以D-和L-丙氨酸是不对称的,两者间有能量的差别.自然界的力只有弱力是宇称不守恒的.在分子物理中,电弱力宇称不守恒是导致D-和L-丙氨酸能差的根源.所有以前的研究都认为L型丙氨酸比D型稳定.但是,最近以Quack[9]和Schwerdtfeger[11]为首的理论物理学家计算了L-丙氨酸在气相和溶液两种状态下,宇称破缺能差与分子构象的关系,提出“D-和L-丙氨酸究竟哪一个稳定”的质疑.由于气相和液相中两面角较难测定,我们用X射线四圆单晶衍射法,测定了270K和250KD和L-丙氨酸的O（1）O（2）C（1）C（2）H（4）的原子坐标,算出了二面角,按照Quack[9]的MC-LR方法,D-和L-丙氨酸宇称破缺能差为1.2 x 10-19Hartree,相当于3.3 x 10-18eV/分子或3.2x10-16kJ·mol-1,从而得出D-丙氨酸能态高于L-丙氨酸的结论.展开更多
文摘一、引言
X射线单晶体衍射仪的英文名称是X-ray single cry stal diffractomet er,简写为XRD.
本仪器分析的对象是一粒单晶体,如一粒砂糖或一粒盐.在一粒单晶体中原子或原子团均是周期排列的.将X射线(如C u的Kα辐射)射到一粒单晶体上会发生衍射,由对衍射线的分析可以解析出原子在晶体中的排列规律,也即解出晶体的结构[1].物质或由其构成的材料的性能是与晶体的结构密切相关的,如金刚石和石墨都是由纯的碳构成的,由于它们的晶体结构不同就有着截然不同的性质.
基金supported in part by Program for New Century Excellent Talents in University of China (No. NCET-10-0133)Innovation Scientists and Technicians Troop Construction Projects of Henan Province (No. 114100510004)
文摘X-ray diffraction （XRD） was used to study the structure of the organic crystallite unit （La, Lo doo2） in coals collected from Henan and Shanxi Provinces. XRD patterns of coal were collected in a step-scan mode （0.1 °/step） over an angular range of 2-90° （20）, allowing 8 s at each step. The structure of the crystallite unit was determined from the Scherrer equation and peak parameters deduced from whole pattern fitting. The results show that the structure of the crystallite unit in coal is mainly controlled by the coal rank. As the coal rank increases the average diameter of a coal crystallite unit （La） increases, the interlayer spacing （doo2） decreases slightly, and the average height of a coal crystallite unit （Lc） increases at first but then decreases. A new diffraction peak from the crystallite unit in coal was found at a low scattering angle in the XRD pattern （2-10~）. This suggests a structure with an inter-layer spacing from 1.9 to 2.8 nm exists in coal crystallites.
文摘A new sodium indium phosphate Na 6In 4[P 7O 24(OH) 5]·4H 2O was synthesized under a mild hydrothermal condition and its structure was determined by means of single-crystal X-ray diffraction methods. The title compound crystallizes in a hexagonal system, space group P6 3, with a= 0.950 23(5) nm, b=0.950 23(5) nm, c=1.694 2(2) nm, α=90°, β=90°, γ=120°, V=1.324 8(2) nm 3, Z=8, structure refined to R=0.052 8 and wR=0.116 5 for 2 134 independent observed reflections. The three-dimensional network structure consists of helical chains formed by apex-sharing polyhedra. The connection of the chains results in 4- and 8-polyhedral rings and cages centered by three indium metal connecting oxygen atoms formed by three 4-rings. The three-connected oxygen atom is firstly observed in indium phosphate systems.
文摘在宇宙开始大爆炸的时候,电荷变号与镜象反射共轭（CP）是对称的.但现在我们的宇宙绝大部分是正物质核子和电子等组成的,所以我们的宇宙是不对称的.D和L-丙氨酸通常称为对映体（enantiomer）,实际上它们并不是由正、反粒子组成的真正的对映体,而是空间反演的,即x--x,y--y,z--z的非对映异构体（diastereoisomer）,所以D-和L-丙氨酸是不对称的,两者间有能量的差别.自然界的力只有弱力是宇称不守恒的.在分子物理中,电弱力宇称不守恒是导致D-和L-丙氨酸能差的根源.所有以前的研究都认为L型丙氨酸比D型稳定.但是,最近以Quack[9]和Schwerdtfeger[11]为首的理论物理学家计算了L-丙氨酸在气相和溶液两种状态下,宇称破缺能差与分子构象的关系,提出“D-和L-丙氨酸究竟哪一个稳定”的质疑.由于气相和液相中两面角较难测定,我们用X射线四圆单晶衍射法,测定了270K和250KD和L-丙氨酸的O（1）O（2）C（1）C（2）H（4）的原子坐标,算出了二面角,按照Quack[9]的MC-LR方法,D-和L-丙氨酸宇称破缺能差为1.2 x 10-19Hartree,相当于3.3 x 10-18eV/分子或3.2x10-16kJ·mol-1,从而得出D-丙氨酸能态高于L-丙氨酸的结论.
