Spectroscopy and spectrograph are terms used to refer to the measurement of radiation Intensity as a function of wavelength and are often used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrograph or spectral analyzers. Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies (colors).
Neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A commonly encountered molecular spectrum Is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives alarm polluted with nitrogen dioxide a reddish brown color. Raleigh scattering Is a spectroscopic scattering phenomenon that accounts for the color of the sky.
Spectroscopic studies were central to the development of quantum mechanics and included Max Plank’s explanation of blackbody radiation, Albert Einstein explanation of the photoelectric effect and Nielsen Boor’s explanation of atomic structure and spectra. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy Is also used in astronomy and remote sensing on earth. Most research telescopes have spectrograph.
The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature and velocity), Theory One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs.. Excitation frequency will have a peak centered at the resonance frequency.
This plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the analogous resonance Is a coupling of two mutant mechanical stationary states of one system, such as an atom, Oval an strongest when the energy of the source matches the energy difference between the two states. The energy (E) of a photon is related to its frequency Non) by E = h
u where h is Plank’s constant, and so a spectrum of the system response vs.. Photon frequency will peak at the resonant frequency or energy.
Particles such as electrons and neutrons have a comparable relationship, the De Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite sonant interactions. Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics.
The hydrogen spectral series in particular was first successfully explained by the Rutherford-Boor quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough. Classification of methods Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways.
Type of irradiative energy Types of spectroscopy are distinguished by the type of irradiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of irradiative energy studied include: Electromagnetic radiation was the first source of energy used for spectroscopic studies. Techniques that employ electromagnetic radiation are typically classified by the wavelength region of the spectrum and include microwave, thereafter, infrared, near infrared, visible and ultraviolet, x-ray and gamma spectroscopy.
Particles, due to their De Broglie wavelength, can also be a source of irradiative energy and both electrons and neutrons are commonly used. For a particle, its kinetic energy determines its wavelength. Acoustic spectroscopy involves radiated pressure eaves. Mechanical methods can be employed to impart radiating energy, similar to acoustic waves, to solid materials. Nature of the interaction Types of spectroscopy can also be distinguished by the nature of the interaction between the energy and the material. These interactions material.
Absorption is often determined by measuring the fraction of energy transmitted through the material; absorption will decrease the transmitted portion. Emission indicates that irradiative energy is released by the material. A material’s blackbody spectrum is a spontaneous emission spectrum determined by its temperature. Emission can also be induced by other sources of energy such as flames or sparks or electromagnetic radiation in the case of fluorescence. Elastic scattering and reflection spectroscopy determine how incident radiation is reflected or scattered by a material.
Crystallography employs the scattering of high energy radiation, such as x-rays and electrons, to examine the arrangement of atoms in proteins and solid crystals. Impedance spectroscopy studies the ability of a medium to impede or slow the transmittance of energy. For optical applications, this is characterized by the index of refraction. Inelastic scattering phenomena involve an exchange of energy between the radiation and the matter that shifts the wavelength of the scattered radiation. These include Raman and Compton scattering.
Coherent or resonance spectroscopy are techniques where the irradiative energy couples two quantum states of the material in a coherent interaction that is sustained by the radiating field. The coherence can be disrupted by other interactions, such as particle collisions and energy transfer, and so often require high intensity radiation to be sustained. Nuclear magnetic resonance (NOR) spectroscopy s a widely used resonance method and ultraist laser methods are also now possible in the infrared and visible spectral regions.
Type of material Spectroscopic studies are designed so that the radiant energy interacts with specific types of matter. Atoms Atomic spectroscopy was the first application of spectroscopy developed. Atomic absorption spectroscopy (AS) and atomic emission spectroscopy (AES) involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to electronic transitions of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states.
Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantization of a sample’s elemental composition. Robert Bunsen and Gustavo Kerchief discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to as Forerunner lines after their discoverer. A comprehensive explanation of the hydrogen spectrum was an early success of quantum mechanics and explained the Lamb shift observed in the hydrogen spectrum led to the development of quantum electrodynamics.
Modern implementations of atomic spectroscopy for studying visible and ultraviolet emission spectroscopy, glow discharge spectroscopy, microwave induced plasma spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include X-ray spectroscopy and X-ray fluorescence (SERF). Molecules The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states.
Molecular spectra can be obtained due to electron spin states (electron paramagnetic resonance), molecular rotations, molecular vibration and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimeter-wave spectral regions; rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and Raman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy.
Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser. Crystals and extended materials The combination of atoms or molecules into crystals or other extended forms leads to the creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, I. E. , broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well.
Pure crystals, though, can have distinct spectral transitions and the crystal arrangement also has an effect on the observed molecular spectra. The regular lattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies. Nuclei Nuclei also have distinct energy states that are widely separated and lead to gamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for NOR spectroscopy.