字幕表 動画を再生する 英語字幕をプリント Ultraviolet visible spectrometry tells us about electronic transitions in atoms and molecules Spectra are produced when it electons in molecules or atoms move from one electronic energy level to another of higher energy. In doing so they absorb energy equal to the gap between the two levels. Compounds that absorb in the visible region such as some transition metal compounds inorganic dyes are colored. Those that absorb only in the ultraviolet region are colorless. Inside a UV visible spectrometer there are usually two light sources, one giving out visible light and one ultraviolet. This one is a tungsten lamp like a car headlamp bulb for the visible region. And this teuterium lamp gives out ultraviolet. This mirror directs light from the appropriate source into the monochromator. This contains a diffraction grating that acts rather like the playing surface of a CD to split the light into it's constituent wavelengths. Different wavelengths correspond to different colours. Red is about 700 nanometers and blue around 400 nanometers. Wavelengths shorter than about 350 nanometers are called ultraviolet. Shorter wavelength light has high-energy. The source produces white light that includes all wavelengths all colors. The instrument scans through the spectrum sending different wavelengths of light through the sample in sequence. This is done by the grating which rotates. A single wavelength passes into the modulator which consists of a rotor with mirrors on it. This chops the light into two beams. One beam passes through the sample cell while the other passes through the reference cell. So the instrument is referred to as a double beam instrument. Both sample and reference beams are directed by mirrors onto a detector. This compares their intensities and send a signal proportional to the ratio of their intensities to the computer that controls the instrument. The logarithm of this ratio gives a quantity called absorbance which is a measure how much light is being absorbed by the sample at that particular wavelength. Ultraviolet visible spectra are usually run on solutions light does not normally pass through solid samples. Here we will run the spectrum of a green food dye. To run the spectrum we place some of the solvent in a sample cuvette to act as a blank, a reference. The cuvette may be made of glass or plastic if only the visible region of the spectrum is required. Quartz cuvettes are needed for work in the ultraviolet range because glass and plastics absorb UV light. We then place a solution of the sample in a second cuvette. The blank and the sample are placed in the sample holders. The lid is closed to prevent light from the laboratory interfering with spectrum. The operator types details such as the wavelength range required and scanning speed into the computer that controls the instrument. He also zeros the instrument at a point where the sample does not absorb and then starts the scan. The spectrum appears on screen, the data is saved on the computer and a hard copy can be printed. The horizontal axis is normally wavelength and the vertical one absorbance which is a measure the amount of light absorbed by the sample. The peaks on the spectrum are the wavelengths of light that are absorbed by the sample and the troughs and where light passes through. So the dye absorbs orange and blue light and lets through green. So it appears green in color
B2 中上級 紫外・可視分光法(UV-Vis (Ultraviolet/Visible Spectroscopy (UV-Vis)) 67 6 Cheng-Hong Liu に公開 2021 年 01 月 14 日 シェア シェア 保存 報告 動画の中の単語