Introduction
The well-known soda-yellow wavelength is 589.3 nm, which is the first spectrum of the sodium spectrum main line. Both alkali metal atoms have similar structures, and the inner layer Z-1 electron with the atomic nucleus is true. The outermost layer has only one price electron, which is similar to the hydrogen atom, and the electron movement is polarized and penetrated throughout The role, causing a large split of the electron energy of different tracks, and the energy level is degenerate to L. In addition, since the electron spindle is different, the energy level of the spin orbit is coupled, so that the energy level of the alkali metal atom is a single layer, other P, D, and F state are double-layer. Depending on the choice of unit price atom spectroscopy, it can be obtained that the main line and the sharp line are the two-wire structure, the diffuse and the baseline system.
Observation Results
Figure 1 shows four line systems of lithium atomic spectroscopy. From Figure 1, it can be seen that the wavelength range of the main line is the widest, and the first one is red, and the rest are in ultraviolet. The line limit is 229.97 nm; the first auxiliary line is in the visible optical zone portion; the first two secondary line series is in the infrared area, the remaining in the visible optical zone, the second line is the same line system, the Bergman line is Infrared areas, other alkali metal atoms have similar spectral lines, only different wavelengths, such as the main line of sodium, is the familiar yellow light, and the wavelength is 589.3 nm.
Atomic Structure
The alkali metal atom is similar to the molecular spectrum of hydrogen atoms, which is similar to that of their atomic structures, although the alkali metal element is extremely different from the nature of the hydrogen element, but they all There is only one outer electron, called price electrons. The full-folding shell electron with the atomic nuclear composition of the nucleus, the price electron is in the central potential field of the atomic real. According to lithium, sodium, potassium, 铷, 铷,, the number of electrons in real, 2, 10, 18, 36, 54, 86, the main amounts of the rails of the valence are N≥2, n ≥ 3, respectively. , N ≥ 4, N ≥ 5, n≥6.
Energy-Level Formula
The energy-level formula of alkali metal atoms and hydrogen atomic similar formula is quantum loss, is a positive number associated with the number of angular momentum quantum L. R It is a constant of the alkali metal. Obviously, the energy level of the alkali metal is not only related to N, but also related to L. The above equation can also be written as z * called a valid nuclear charge. Taking lithium as an example, four line formulas are
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First secondary line
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second auxiliary tab |
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Bergman Line |
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The line formula of other alkali metal atoms is similar. Figure 2 is a schematic diagram of the energy level and spectral line of a lithium atom.
When a spectrophotometer of the resolution is to observe a spectral line of an alkali metal atom, it will be seen from two or three sharp lines, which is called the double structure of the spectral line (or The double double structure is sometimes referred to as the fine structure of the alkali metal atom spectrum. For example, the first strip of the sodium spectrum main line is composed of two lines of 589.0 nm and 589.6 nm. The average value is 589.3 nm, and the spectrum of all alkali metal atoms has a similar double structure.
The dual structure of the alkali metal atomic line is due to the results of electron spin and track motion interaction, and the self-rotating angle of electrons is equal to that is, the number of spin quantum s = 1/2. Also because the amount of electron spin angle is only two orientations with respect to the orbit angle, the total angular momentum quantum digital alkali metal atom is only one price electron, and the total angle of the full-enclosure layer is movable. Zero, the momentum of the price electron is equal to the total angular momentum of the atom.
corresponds to the two orientations of spin, the electron spin and track interactions have caused energy-level splitting to two, so the spectroscopy of alkali metal atoms is a double layer, for л = 0, 1 2, 3, ... S, P, D, F, ... use symbol 2S┩, 2P┩, 2D 崰, 2D 嵻, ..., in which the upper corner corner 2 represents the number of levels of the energy level, the lower right corner The standard represents the J value, theoretical calculation shows that the interval between the two-layer energy levels between the alkali metal atom can be expressed as
in which
α is fine structure constant. It can be seen from the above formula that δ is reduced with N, л, and the increase of z * is increased quickly, which is in line with the experimental observation.
Atomic spectrum is due to the transition between electrons between different energy levels. Depending on the selection of radiation transition: Δл = ± 1, ΔJ = 0, ± 1. Therefore, each spectral wire of the alkali metal atom can be represented as follows:
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second auxian system |
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First secondary wire |
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< P> Bergmannite ||
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where the arrow indicates the transition between the two levels, that is, a spectral line. The left end of the arrow indicates an caption, the n value is changed; the right end indicates the lower energy level, and its n value is fixed. For example, for the main line of lithium, the right end should be 22S ┩, ie the base state n = 2 of lithium; the sodium-based n = 3. The energy level and transition process of sodium atoms is shown in Figure 3.
As can be seen from Figure 3, the main line system and the second secondary wire are composed of two-wire; the first secondary lineage and the Bergman line (not shown) consists of three wires. In the alkali metal spectrum, in addition to the double line distance of the lithium atom is too small, the two-wire structure of other alkali metal spectroscopy is clear. Taking the first pair of alkali metal main lines as an example, the order of sodium, potassium, 铷,,, is 0.6 nm, 3.4 nm, 14.7 nm, 42.2 nm, the first pair of visible and cesium, respectively. Far.
The ultra-fine structure of the alkali metal spectrum can be referred to in the superfine structure of atomic spectroscopy.