有机光谱化学分析 (48).pdf

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1、P1:Hello everyone,welcome to this lecture-organic spectroscopic analysis.大家好，欢迎学习有机光谱分析课程。P2:In this graph,we have learned to radio waves for NMR spectroscopic,infrared for transitions of vibrational states,UV for transitions of valence electrons,and X-ray for the transition of core electrons.And in

2、 this lecture,we are going to study X-ray diffraction.在此图中，我们已经学习了用于 NMR 光谱的无线电波，（对应于）振动能级跃迁的红外光，价电子跃迁的紫外以及内层电子跃迁的 X 射线。在这一节课中，我们将学习 X 射线衍射。P3:As we mentioned in the MS chapter,J.J.Thomson discovered the electrons by a cathode tube.正如我们在质谱 MS 章节中提到的，汤姆逊（J.J.Thomson）通过阴极射线管发现了电子。P4:As we all know tha

3、t Roentgen discovered X-rays,Roentgens wife had placed her hand in the path of X-rays,which Roentgen created by beaming an electron ray energy source onto a cathode tube.众所周知，伦琴发现了 X 射线。伦琴通过在阴极管中发射电子射线得到了 X 射线，而伦琴的妻子将她的手放在 X-射线的路径上，得到了手骨的照片。Roentgens discovery of these mysterious rays capable of pro

4、ducing an image on a photographic plate excited scientists of his day,including Becquerel.伦琴发现的这些“神秘”射线能够在照相底片上产生图像，这激发了当时包括贝克勒尔（Becquerel）在内的科学家们的兴趣。Becquerel found that,while the phenomena of fluorescence and phosphorescence had many similarities to each other and to X-rays,they also had important

5、 differences.贝克勒尔发现，尽管荧光现象和磷光现象以及与 X 射线有许多相似之处，但它们也具有重要的区别。While fluorescence and X-rays stopped when the initiating energy source was halted.Much to his Becquerels surprise,the plates were exposed during storage by invisible emanations from the uranium.当激发能量源停下时，荧光和 X 射线亦停止产生。令贝克勒尔大为惊讶的是，这些底片在储存过程中

6、被铀发射的无形射线曝光了。The emanations did not require the presence of an initiating energy source-the crystals emitted rays on their own!Although Becquerel did not pursue his discovery of radioactivity,others did and in doing so,changed the face of both modern medicine and modern science.这种辐射不需要存在激发能源（铀）晶体自行发

7、出射线！尽管贝克勒尔并未追寻他对放射性的发现，但其他人却这样做了，这也改变了现代医学和现代科学的面貌。P5:Atomic particles,Rutherfords work showed that consisted primarily of empty space surrounding a well-defined central core called a nucleus.卢瑟福的工作表明，原子是由主要是空白的空间围绕中心核（称为原子核）组成。In a long and distinguished career,Rutherford laid the groundwork for th

8、e determination of atomic structure.（在其漫长而杰出的职业生涯中，卢瑟福为确定原子结构奠定了基础。）In addition to defining the planetary model of the atom,he showed that radioactive elements undergo a process of decay over time.（除了定义原子的行星模型外，他还表明放射性元素会随着时间的流逝而衰减。）Taken together,the work of Becquerel,the Curies,Rutherford and othe

9、rs,made modern medical and scientific research more than a dream,they made it a reality with many applications.总的来说，贝克勒尔，居里夫人，卢瑟福和其他人的共同努力使现代医学和科学研究不仅仅是梦想，他们使许多应用成为现实。A look at the use of isotopes reveals just some of the ways in which the pioneering work of these scientists has been utilized.同位素的使用

10、就是这些科学家开创性工作的一些应用。P6:Seventeen years after the discovery of X-rays,in 1912,the German physicist Laue discovered and recorded the diffraction phenomenon that occurred when X-rays passed through crystals.发现 X 射线 17 年后，在 1912 年，德国物理学家劳厄（Laue）发现并记录了 X 射线透过晶体时发生的衍射现象。P7:Sir William Henry Bragg and his so

11、n Sir William Laurence Bragg,determined the first mineral structure which is(NaCl)from XRD.威廉 亨利 布拉格爵士和他的儿子威廉 劳伦斯 布拉格爵士，用 XRD确定了第一个晶体结构（NaCl）。P8:In Braggs law,incoming X-rays diffract from the crystal planes.Reflections must be in phase for a detectable signal.根据布拉格定律，入射的 X 射线从晶面发生衍射。散射线必须同相才能检测到信号（

12、相长干涉）。Once we know that the spacing between planes d,we can work out the lattice parameters.Measurement of critical angle c allows computation of interplanar spacing d.一旦知道了晶面之间的间距 d，就可以计算出晶格参数。而由衍射角度的测量也可计算晶面间距 d。P9:X-rays are electromagnetic radiation occupying the spectrum from about 10-2 to 102

13、in wavelength.X 射线是电磁辐射，波长范围从 10-2到 102.P10:X-rays can be described in 2 ways，Electromagnetic wave and Particle or photon with Energy proportional to frequency.X 射线可以用两种方式来描述：电磁波和能量与频率成正比的粒子或光子。P11:X-rays are produced when high energy electrons bombard a metal target,interacting with its atoms.（高能电子

14、轰击金属靶并与其原子相互作用时会产生 X 射线。）The potential difference across the x-ray tube accelerates the electrons from the cathode to the anode,increasing their kinetic energy as(KE).X 射线管上的电势差使电子从阴极加速到阳极，从而增加了它们的动能（KE）。The potential difference across the tube may not be constant(hence use of the term kVp for peak)

15、,therefore the amount of kinetic energy gained by each electron may differ.整个电子管的电位差可能不是相同的（用 kVp 表示峰），因此每个电子获得的动能可能会不同。P12:An x-ray machine,like that used in a doctors or a dentists office,is really very simple.Inside the machine is an x-ray tube.X 射线装置，比如在医生或牙医诊所中使用的那些，其实非常简单。机器内部是一个 X 射线管。An elec

16、tron gun inside the tube shoots high energy electrons at a target made of heavy atoms,such as tungsten.X-rays come out because of atomic processes induced by the energetic electrons shot at the target.管内的电子枪向由钨等重原子制成的靶发射高能电子。X 射线是由于高能电子轰击靶材而引起的原子过程而产生的。P13:“There are two different atomic processes t

17、hat can produce x-ray photons.One is called“braking radiation”.The other is called“characteristic radiation”.“有两种不同的原子过程可以产生 X 射线光子。一种称为“韧致辐射”。另一个称为“特征辐射”。P14:Binding energy is the energy which binds the electron to the nucleus It is the energy that must be supplied to the electron in order to remov

18、e it from its orbital shell.结合能是将电子结合到原子核的能量，是为了将电子从其轨道中移出，必须提供的能量。P15:Excitation results in an outer shell Electron gaining energy&being raised to a higher level.Heat is produced as the electron falls back into its original path.The filament electron may repeat this process many times 激发导致外层电子获得能量并

19、跃迁到更高的能级。当电子回到起始位置时会产生热量。灯丝电子（阴极电子）可以多次重复此过程 P16:Outer shell electron ejected from target atom,Ionisation takes place.Results in an outer shell electron being completely removed from the target atom.This type of interaction may cause the target material to heat up.外层电子飞出靶材原子，发生电离。导致外层电子从靶材原子中完全脱离。这种

20、相互作用可能导致靶材变热。P17:Inner shell electron ejected from atom,Electron falls to occupy vacancy and burst of x-ray emission 内层电子从原子中射出，外层电子跃迁占据空位并发射 X 射线 P18:In 1913,Henry Moseley discovered that the wavelength(energy)of an X-ray depended upon the nuclear charge of an atom 1913 年，亨利 莫赛莱（Henry Moseley）发现 X

21、射线的波长（能量）取决于原子的核电荷。P19:The K and K transitions are the most likely to occur,producing x-ray photons of about 58 and 68 keV.（钨）最有可能发生 K 和 K跃迁，产生58 和68 keV 的 X 射线。P20:Henry Moseley discovered that the wavelength(energy)of an X-ray depended upon the nuclear charge of an atom in 1913.亨利 莫赛莱（Henry Mosele

22、y）在 1913 年发现 X 射线的波长（能量）取决于原子的核电荷。Until Moseleys work,“atomic number”was merely an elements place in the periodic table,and was not known to be associated with any measureable physical quantity.在莫赛莱（Moseley）的工作之前，“原子序数”仅是元素周期表中元素的位置，而不与任何可测量的物理量有关。P21:The incoming electron transfers sufficient energ

23、y to remove an inner shell electron from its atom in the target.入射电子传递足够的能量以将内层电子从靶原子中移除。In order for this to occur the electron must possess energy at least as great as the binding energy of the inner shell.为了使这种情况发生，电子必须具有至少与内层电子的结合能一样大的能量。The inner shell vacancy is quickly filled by an electron f

24、alling inwards from a shell further out from the nucleus 内层空位迅速被从离原子核更远的电子跃迁所填充 This transition is accompanied by a burst of electromagnetic radiation with energy equal to the difference in binding energies of the two shells.这种跃迁伴随着电磁辐射的爆发，其能量等于两层的结合能之差。This type of x-ray production is termed charac

25、teristic because the exact photon energy is characteristic of the element of which the target is made.这种类型的 X 射线产生称为特征射线，因为光子的确切能量是靶材所特有的。P22:In summary,characteristic x-rays are produced by transitions of orbital electrons from outer to inner shells.（总而言之，特征 X 射线是由电子从外层到内层的跃迁产生的。）Since the electron

26、 binding energy for every element is different,the characteristic x-rays produced in the various elements are also different.（由于每种元素的电子结合能不同，各种元素产生的特征 X 射线也不同。）This type of x-radiation is called characteristic radiation,because it is characteristic of the target element.（这种 x 射线称为特征辐射，因为它是靶材所特有的。）Th

27、e effective energy of characteristic x-rays increases with increasing atomic number of the target element.特征 X 射线的有效能量随着靶材原子序数的增加而增加。P23:Characteristic x-rays contribute less than 10%of an x-ray beam.The majority of x-ray production results from inelastic collisions of incoming electrons with the nu

28、clei of the target atoms.特征 X 射线的贡献了不到 10的 X 射线。X射线的产生主要是由于入射电子与靶材原子核的非弹性碰撞造成的。P24:The incoming electron passes very close to the nucleus of a target atom.The attraction causes the electron to deviate in its course.当入射电子从非常靠近靶材的原子核的地方穿过时，（原子核的）吸引力使电子发生偏离。The sudden change of direction stimulates the

29、 electron to release energy in the form of a photon of electromagnetic radiation.方向的突然改变会激发电子以电磁辐射的形式释放能量。The emission of radiation results in a reduction in the electrons kinetic energy causing it to slow down.辐射的发射导致电子的动能降低，从而使其减速。P25:The energy of the radiation depends on the degree of deviation

30、the electron suffers.辐射的能量取决于电子的偏离程度。In an extreme case the electron may actually be brought to rest.Thus the photon energy can be one of any value from zero up to a maximum equal to the initial kinetic energy of the incoming electron.在极端情况下，电子实际上可能会停下来。因此，光子能量可以是从零到最大等于入射电子的初始动能的任何值。This gives rise

31、 to a continuous spectrum of x-radiation and is known as braking(Bremsstrahlung)radiation.这会产生连续的 x 射线谱，称为韧致辐射。P26:Inelastic processes are much more likely to occur than characteristic or braking processes 与特征或韧致辐射过程相比，发生非弹性过程的可能性更大。Less than 1%of the energy in a x-ray tube is converted into x-rays(

32、the rest is heat).X 射线管中只有不到 1的能量被转换为 X 射线（其余为热量）。At higher voltages the efficiency is higher&relatively less heat is produced.在较高电压下，效率较高，并且产生的热量相对较少。Characteristic x-ray production cannot take place at all if the x-ray tube voltage is insufficient to give electrons enough energy to remove an inner

33、 shell electron from the target atom.如果 X 射线管电压不足以使电子有足够的能量从目标原子中除去内层电子，则根本不会产生特征性 X 射线。P27:With a tungsten target,voltages below about 68 kV cannot produce tungsten characteristic radiation.In other materials,such as molybdenum,the voltage value required to produce characteristic radiation is much

34、less(approximately 27 kV).使用钨靶时，低于 68 kV 的电压不能产生钨的特征辐射。在其他材料（例如钼）中，产生特征辐射所需的电压值要小得多（约27 kV）The amount of heat produced within an x-ray tubes can cause problems.X 射线管内产生的热量可能会引起问题。OK.Thats for todays lesson of X-ray diffraction.Thank you for watching!好的。今天的 X 射线衍射课程就到这里。谢谢观看！Ok,thats todays lecture.We will Continue to learn X-ray diffraction in the next class.see you!好了，这就是今天的内容。下节课我们将继续学习 x 射线衍射。再见！