khí quyển sao p7

IS quang phổ nguyên tử, tất nhiên, về một chủ đề rộng lớn, và có ý định là Không có trong chương này ngắn gọnCố gắng để trang trải của trường A như vậy rất lớn với bất kỳ mức độ Tính đầy đủ, và đó là không dự kiếnđể phục vụ như là một khóa học chính thức trong quang phổ. Như vậy là một nhiệm vụ cho một ngàn trang sẽ làm cho mộtTốt bắt đầu. Mục đích, Thay vào đó, là để tóm tắt Một số từ và ý tưởng đầy đủ choNhu cầu của các sinh...
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khí quyển sao p7 1 CHAPTER 7 ATOMIC SPECTRA7.1 Introduction Atomic spectroscopy is, of course, a vast subject, and there is no intention in this brief chapterof attempting to cover such a huge field with any degree of completeness, and it is not intendedto serve as a formal course in spectroscopy. For such a task a thousand pages would make agood start. The aim, rather, is to summarize some of the words and ideas sufficiently for theoccasional needs of the student of stellar atmospheres. For that reason this short chapter has amere 26 sections. Wavelengths of spectrum lines in the visible region of the spectrum were traditionallyexpressed in angstrom units (Å) after the nineteenth century Swedish spectroscopist AndersÅngström, one Å being 10−10 m. Today, it is recommended to use nanometres (nm) for visiblelight or micrometres (µm) for infrared. 1 nm = 10 Å = 10−3 µm= 10−9 m. The older word micronis synonymous with micrometre, and should be avoided, as should the isolated abbreviation µ.The usual symbol for wavelength is λ. Wavenumber is the reciprocal of wavelength; that is, it is the number of waves per metre. Theusual symbol is σ, although ~ is sometimes seen. In SI units, wavenumber would be expressed ν -1 -1in m , although cm is often used. The extraordinary illiteracy a line of 15376 wavenumbersis heard regrettably often. What is intended is presumably a line of wavenumber 15376 cm-1.The kayser was an unofficial unit formerly seen for wavenumber, equal to 1 cm-1. As some wagonce remarked: The Kaiser (kayser) is dead! It is customary to quote wavelengths below 200 nm as wavelengths in vacuo, but wavelengthsabove 200 nm in standard air. Wavenumbers are usually quoted as wavenumbers in vacuo,whether the wavelength is longer or shorter than 200 nm. Suggestions are made from time totime to abandon this confusing convention; in any case it is incumbent upon any writer whoquotes a wavelength or wavenumber to state explicitly whether s/he is referring to a vacuum orto standard air, and not to assume that this will be obvious to the reader. Note that, in using theformula n1λ1 = n2λ2 = n3λ3 used for overlapping orders, the wavelength concerned is neither thevacuum nor the standard air wavelength; rather it is the wavelength in the actual air inside thespectrograph. If I use the symbols λ0 and σ0 for vacuum wavelength and wavenumber and λ and σ forwavelength and wavenumber in standard air, the relation between λ and σ0 is 1 λ= 7.1.1 nσ 0Standard air is a mythical substance whose refractive index n is given by 2 240603. 0 1599. 7 , ( n − 1).107 = 834. 213 + + 7.1.2 130 − σ 0 38. 9 − σ 2 2 0where σ0 is in µm-1. This corresponds closely to that of dry air at a pressure of 760 mm Hg andtemperature 15o C containing 0.03% by volume of carbon dioxide.To calculate λ given σ0 is straightforward. To calculate σ0 given λ requires iteration. Thus thereader, as an exercise, should try to calculate the vacuum wavenumber of a line of standard airwavelength 555.5 nm. In any case, the reader who expects to be dealing with wavelengths andwavenumbers fairly often should write a small computer or calculator program that allows thecalculation to go either way. Frequency is the number of waves per second, and is expressed in hertz (Hz) or MHz or GHz,as appropriate. The usual symbol is ν, although f is also seen. Although wavelength andwavenumber change as light moves from one medium to another, frequency does not. Therelation between frequency, speed and wavelength is c = νλ0, 7.1.3where c is the speed in vacuo, which has the defined value 2.997 924 58 % 108 m s-1. A spectrum line results from a transition between two energy levels of an atom The frequencyof the radiation involved is related to the difference in energy levels by the familiar relation hν = ∆E, 7.1.4where h is Plancks constant, 6.626075 % 10-34 J s. If the energy levels are expressed in joules,this will give the frequency in Hz. This is not how it is usually done, however. What is usuallytabulated in energy le ...