As spectroscopy of physical chemistry, what are the similarities and differences in the direction of

In the field of analytical chemistry, the understanding of spectrum is the relationship between two variables: light intensity and wavelength. Of course, this function is generally expressed in the form of a curve, with the abscissa being the wavelength and the ordinate being the intensity.

Chemistry is the study of the composition, structure, and properties of matter, and analytical chemistry is a method of obtaining this information. Specifically, it is to study the relationship between other measurable quantities and the composition, structure, and properties of the substance, so as to derive data on composition and structure based on the measurement results. The reason why spectroscopy can be used in analytical chemistry is that in the spectrum, the two characteristic quantities of wavelength and intensity are measurable quantities, and both have a corresponding relationship with the composition, structure and properties of substances.

And, more importantly, some of the correspondence is metrologically characteristic. For each correspondence with metrological characteristics, a spectral analysis method is derived accordingly. Let's illustrate with some examples:

For atomic emission spectroscopy, the wavelength generally corresponds to which elements are in the substance, so qualitative analysis is carried out according to this relationship in analytical chemistry. The research method in structural chemistry is to find a pure elemental element, measure its wavelength, and then perform quantum chemistry calculations (probably so, I really don't understand this aspect). But analytical chemistry does the other way around, deriving the elemental composition from the measured wavelengths.

The atomic orbitals of an element determine the wavelength, that is, the derivation process of "element = > wavelength". However, this derivation process is sufficient but not necessary, that is, the aforementioned metrological characteristics are not satisfied, and it is not a one-to-one correspondence.

One element corresponds to multiple wavelengths, and the same wavelength can be used for different elements. Therefore, in analytical chemistry, it is necessary to consider what means can establish a strict one-to-one correspondence, or which spectral lines can be qualitatively qualified with a high degree of confidence and will not be misjudged. <>

I am a physicist, and when I was in college, I also took some courses in analytical chemistry and instrumental analysis. Let's talk about what I don't understand, the spectroscopy of analytical chemistry, as soon as I heard it, I thought of infrared absorption spectroscopy, Fourier transform infrared spectroscopy, and Raman spectrometer (there are many spectral testing methods of major analysis and testing platforms, which can be understood); The characteristic is that starting from a mature commercial instrument, using some very mature methods, doing exactly the same operation on different substances, extracting information for analysis, no matter what sample, taking it is a pair, and then analyzing the data to summarize the phenomena and laws. Spectroscopy in physicochemistry, as soon as I hear this, I want to build various devices, resonance-enhanced multiphoton ionization (REMPI), laser-induced fluorescence (LIF), and cavity ring-down spectroscopy (CRDS); Infrared spectroscopy (IR) and Raman spectroscopy are also often played together.

One thing to say, this is all a way to tell you, the device is built by itself; He also uses well-established commercial spectroscopy instruments, such as infrared and Raman spectroscopy, but it is for a chemical reaction system, constantly changing the reaction regulation, and this commercial instrument is only a means of characterization on the device; I think differentiation is more concerned with measuring a result, and materialization is more concerned with a reaction process. The most popular feeling, differentiated spectroscopy, is to take a mature machine, keep changing various samples, measure it to see what it is, and analyze what functional groups and components it is; Physicochemical spectroscopy is, I give you a molecule, such as H2, and you measure the precise position of each vibration v, rotation j, and even angular quantum m. For example, CH4, each vibration mode, combined vibration, what bending and tensile vibration, fundamental frequency, and pan frequency are measured. <>

Atomic emission spectroscopy, the basic theories of which have been well established in spectroscopy and structural chemistry for a long time, but these theories are aimed at pure matter, rarefied gases, and thermodynamic equilibrium. In an ideal thermodynamic equilibrium system, regardless of the interaction between particles, how many ground states, how many excited states, how many neutral atoms, how many first-order ionizations, how many second-order ionizations, what are the transition probabilities, how many photons are emitted, and how many photons are self-absorbed, ...... are consideredThese can be calculated precisely, so there is a strict quantitative relationship between the number of atoms and the intensity of the emission line. However, analytical chemistry is often faced with a mixture of condensed matter, such as a bucket of water or a stone, and the quantitative relationship in this is not as simple as the theory says, and the accuracy is greatly reduced.

Therefore, analytical chemistry is not concerned with the basic theory of emission spectroscopy, but with physics. Analytical chemistry is also not very concerned with the accurate measurement of wavelength and light energy, which is studied by people who are engaged in optical instruments. <>

Spectrum

Spectrum is a pattern in which the monochromatic light dispersed by dispersion is arranged in sequence according to the wavelength (or frequency) after the polychromatic light is divided by a dispersive system (such as a prism or grating).