Theory of Molecular Spectroscopy

Basic Theory of Molecular Spectroscopy

From the mid- 1950s, JASCO has been researching and developing instruments and applications for some of the most important areas of molecular spectroscopy, including infra-red (FTIR), Raman, fluorescence, UV-visible/near infra-red, and chiral spectroscopy.

The evaluation of chirality has become an important area in molecular spectroscopy because it is used in the development of biomolecules that are useful as new medicines, and for materials that can be used in novel technologies for applications in material science. Chiral spectroscopy includes diverse techniques such as optical rotation dispersion (ORD) and polarimetry, circular dichroism (CD) – both electronic and vibrational (VCD), as well as circularly polarized luminescence (CPL).

FTIR IconFTIR Spectroscopy

FTIR is concerned with the vibration of molecules.  Each functional group has its own discrete vibrational energy which can be used to identify a molecule through the combination of all of the functional groups. This makes FTIR microscopy ideal for sample ID, multilayer film characterization, and particle analysis.

Raman IconConfocal Raman Microscopy

This technique offers a number of significant advantages over other spectroscopic or optical microscopy techniques, as it can be used for chemical or molecular analysis encompassing depth profiling and microscopic mapping of samples with spatial resolution as little as 1 μm.

IRT IconFTIR Microscopy

Infrared spectroscopy is used to probe the the vibration of bonds in a variety or organic and inorganic molecules . This makes FTIR microscopy ideal for imaging materials using functional group(s),  sample identification , multilayer film characterization, and particle analysis.

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Circular Dichroism Spectroscopy

Circular dichroism spectroscopy (CD) is the essential analytical technique for probing structure of bio- macromolecules such as proteins and nucleic acids. As well as to analyze chirality in small molecules through their optical activity. Recently solid state CD has been used to characterize chiral materials such as polymer films.

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Vibrational Circular Dichroism Spectroscopy

Vibrational circular dichroism (VCD) is a spectroscopy technique that can probe the vibrations of chiral bonds using light in the infrared region. This is distinguished from electronic circular dichroism (ECD or CD), which focuses on absorption of electrons, typically at shorter wavelengths with higher energy.

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Circularly Polarized Luminescence

Recently, circularly polarized luminescence (CPL) spectroscopy has been attracting increased attention. Whereas ECD spectroscopy provides information about the structure of optically active substances in the ground electronic state, CPL spectroscopy provides information about excited states. The two methods are therefore complementary to each other.

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UV/Visible Spectroscopy

UV-Visible/NIR spectroscopy can be divided into ultraviolet, visible, and near-infrared regions of the spectrum, depending on the wavelengths used. since its frequency is close to the overtone frequency of many natural vibrations, weak substance-specific absorption bands can be detected. It can therefore be used for non-destructive measurements, such as determining the sugar, lipid, protein content of foodstuffs and for identifying medicinals.

ATR Colored Icon Small


There are various FTIR methods that can be used to identify foreign material or contaminants. FTIR microscopy is used for foreign material where the size is in the order of few microns, but when a sample with foreign material can be observed by the naked eye, the particle type is typically greater than several hundred microns and does not require an FTIR microscope.  An ATR FTIR method may be a suitable alternative and offers advantages such as minimal sample preparation, non-destructive measurement, and easy handling.

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Fluorescence Spectroscopy

Fluorescence spectroscopy is routinely used for studying structural changes in conjugated systems, aromatic molecules, and rigid, planar compounds due to alterations in temperature, pH, ionic strength, solvent, and ligands.