吸收光谱与发射光谱
物种的吸收和发射光谱有助于识别这些物种并提供有关它们的大量信息。当将物种的吸收和发射光谱放在一起时,它们会形成连续光谱。
什么是吸收光谱?
吸收光谱是在吸光度和波长之间绘制的图。有时,也可以在X轴中使用频率或波数而不是波长。在某些情况下,Y轴也将对数吸收值或传输值也用于Y轴。吸收光谱是给定分子或原子的特征。因此,它可以用于识别或确认特定物种的身份。我们的眼睛以这种特殊的颜色可见彩色化合物,因为它吸收了可见范围的光。实际上,它吸收了我们看到的颜色的互补颜色。例如,我们将一个物体视为绿色,因为它吸收了可见范围的紫色光。因此,紫色是绿色的互补色。同样,原子或分子也从电磁辐射中吸收某些波长(这些波长不一定在可见范围内)。 When a beam of electromagnetic radiation passes through a sample containing gaseous atoms, only some wavelengths are absorbed by the atoms. So when the spectrum is recorded, it consists of a number of very narrow absorption lines. This is known as an atomic spectrum, and it is characteristic to a type of atom. The absorbed energy is used to excite ground electrons to upper levels in the atom. This is known as electronic transition. The energy difference between the two levels is supplied by the photons in the electromagnetic radiation. Since the energy difference is discreet and constant, the same kind of atoms will always absorb the same wavelengths from the given radiation. When molecules are excited with UV, visible and IR radiation, they undergo three different types of transitions as electronic, vibrational and rotational. Because of this, in molecular absorption spectra, absorption bands appear instead of narrow lines.
什么是发射光谱?
通过给出能量,原子,离子和分子可以激发到更高的能级。激发状态的寿命通常很短。因此,这些激发的物种必须释放吸收的能量并恢复基态。这被称为放松。能量的释放可能是作为电磁辐射,热量或两种类型的。释放的能量与波长的图被称为发射光谱。每个元素都有独特的发射光谱,就像它具有独特的吸收光谱一样。因此,来自源的辐射可以通过发射光谱来表征。当辐射物种是在气体中良好分离的个体原子颗粒时,就会发生线光谱。由于分子的辐射,带光谱发生。
吸收和发射光谱之间有什么区别? •吸收光谱给出了波长,a species would absorb in order to excite to upper states. Emission spectrum gives the wavelengths a species would release when coming back to the ground state from the excited state. •在向样品提供辐射时,可以记录吸收光谱,而在没有辐射源的情况下,可以记录发射光谱。 |
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