The Schumann–Runge bands refer to a set of molecular absorption bands associated with the electronic transitions of molecular oxygen (O₂) and, to a lesser extent, ozone (O₃). These bands are named after the German physicists Hermann Schumann and Wilhelm Runge, who studied these phenomena in the early 20th century. The Schumann–Runge bands occur in the ultraviolet region of the electromagnetic spectrum, usually between 175 nm and 205 nm.

The Society for Applied Spectroscopy (SAS) is a professional organization that focuses on the field of spectroscopy, which is the study of the interaction between matter and electromagnetic radiation. Founded in 1947, the society aims to promote and advance the understanding and application of spectroscopic techniques across various disciplines, including chemistry, biology, and materials science. SAS provides a platform for researchers, educators, and professionals to share knowledge, collaborate, and network.

The Sommerfeld–Kossel displacement law is important in the field of atomic physics and was proposed by Arnold Sommerfeld and Friedrich Kossel. It describes the behavior of electrons in atomic systems, particularly in relation to electron transitions and the emission or absorption of photons when electrons occupy different energy levels. In essence, the law states that the amount of energy absorbed or emitted by an atom when an electron transitions between two energy levels is proportional to the difference in energy between those levels.

The Shpolskii matrix refers to a specific type of optical matrix used in the field of spectroscopy, particularly in the study of luminescent materials. It is named after the Russian scientist A. Shpol'skii, who made significant contributions to the understanding of molecular interactions in solid-state systems.

Siegbahn notation is a system used in the field of spectroscopy to designate electronic transitions and the energy levels of atoms, particularly in x-ray spectroscopy. Named after the Swedish physicist Kai Siegbahn, who was awarded the Nobel Prize in Physics in 1981 for his work in this area, the notation provides a systematic way to label the various electron transitions that occur when inner-shell electrons are ejected from an atom.

Single-molecule experiments are techniques used in various fields of scientific research—particularly in biophysics and nanotechnology—that allow scientists to study individual molecules rather than bulk populations. This approach can provide detailed information that is often obscured in traditional ensemble measurements, where the average behavior of many molecules is studied.

Single colour reflectometry is a method used primarily in the field of optical measurements and material characterization. It involves the reflection of a single wavelength (or color) of light from a surface or material to analyze its properties. This technique is often used to characterize thin films, coatings, surfaces, and other materials. ### Key Components and Principles: 1. **Light Source**: A monochromatic light source (such as a laser or LED) emits light of a specific wavelength.

Singlet fission is a photophysical process in which a single excited state (singlet) of a molecule splits into two triplet states. This process can occur in certain organic molecules, particularly those that have favorable exciton interactions and molecular structures. Here’s a more detailed breakdown of the phenomenon: 1. **Initial Excitation**: When a molecule absorbs a photon, it can transition from its ground state (S0) to an excited singlet state (S1).

Site-directed spin labeling (SDSL) is a biophysical technique used to study the structure and dynamics of proteins and other biomolecules at the atomic level. It involves the introduction of a spin label—a stable free radical—at a specific site in a protein or biomolecule. This label can be introduced to a desired location within the protein using genetic engineering techniques, often by substituting a specific amino acid residue with a cysteine that can then be labeled with a spin label.

The Book of Squares, also known as "Liber Quadratorum," is a mathematical work attributed to the Persian mathematician al-Khwarizmi, who lived during the 9th century. The text is notable for its systematic approach to solving quadratic equations and is one of the earliest known works that dealt with algebra in a comprehensive manner.

Specific Ultraviolet Absorbance (SUVA) is a measure used in water quality analysis, particularly in the study of natural organic matter (NOM) in water sources such as rivers, lakes, and drinking water supplies. It provides insight into the concentration and characteristics of dissolved organic carbon (DOC) in water.

Spectral resolution refers to the ability of an instrument to distinguish between different wavelengths or frequencies of electromagnetic radiation. It is a critical parameter in various fields, including spectroscopy, astronomy, and remote sensing, as it determines how finely a spectrum can be resolved. Spectral resolution is commonly defined in terms of the wavelength (or frequency) at which a spectrum can be divided into distinct components.

A **spectral signature** refers to the unique pattern of reflectance or emittance of electromagnetic radiation (light) from an object or material across different wavelengths of the electromagnetic spectrum. Each material has a distinct spectral signature that can be used to identify and differentiate it from other materials. ### Key Points about Spectral Signatures: 1. **Electromagnetic Spectrum**: Spectral signatures are typically measured across various wavelengths, which may include ultraviolet, visible light, infrared, and microwave ranges.

Spectrochemistry is a branch of chemistry that studies the interaction between matter and electromagnetic radiation. It involves the use of various spectroscopic techniques to analyze the composition, structure, and properties of substances based on their absorption, emission, or scattering of light.

Spectral Energy Distribution (SED) is a representation of the energy emitted by an astronomical object, such as a star, galaxy, or any other celestial body, as a function of frequency or wavelength. It provides a comprehensive overview of the object's electromagnetic radiation across a range of wavelengths, from radio waves to gamma rays. The SED is typically plotted with frequency (or wavelength) on the x-axis and the energy flux (or intensity) on the y-axis.

A spectral line is a dark or bright line in a spectrum, representing the absorption or emission of light at specific wavelengths by atoms or molecules. Spectral lines occur when electrons in an atom or molecule transition between energy levels; they either absorb or emit photons with wavelengths that correspond to the energy difference between those levels.

Spectral line ratios refer to the comparison of the strengths (or intensities) of different spectral lines that emerge from a source, often as a result of atomic or molecular transitions. These ratios provide valuable information about the physical conditions in the emitting region, such as temperature, density, chemical composition, and excitation mechanisms.

A spectral line shape refers to the profile or distribution of intensity (or another measurable quantity) of light or other electromagnetic radiation as a function of frequency (or wavelength) around a specific transition frequency associated with an atomic or molecular transition. The shape of the spectral line can provide significant information about the physical conditions surrounding the emitting or absorbing species, as well as the processes that produce the radiation.

Spectroelectrochemistry is an interdisciplinary field that combines electrochemistry and spectroscopy to study the properties and behaviors of chemical species at electrochemical interfaces. It involves the simultaneous application of electrochemical techniques and spectroscopic methods to obtain detailed information about the electronic, molecular, and ionic states of species involved in redox processes.