Spectroscopy: Electromagnetic Radiation and Matter Interaction

Flashcards covering key vocabulary and concepts related to spectroscopy, electromagnetic radiation, its properties, and interactions with matter.

Spectroscopy

The study of the interaction between electromagnetic radiation and matter, covering atomic and molecular aspects.

Electromagnetic Radiation (EMR)

A form of energy with both wave and particle properties, including ultraviolet, visible, infrared, microwave, and radio waves.

Period (p)

The time required for one cycle of a wave to pass a fixed point in space.

Frequency (ν or f)

The number of cycles of a wave that pass a fixed point in space per second, measured in Hz or s-1.

Amplitude (A)

The maximum length of the electric vector in a wave, representing the maximum height of the wave.

Wavelength (λ)

The distance between two identical adjacent points in a wave, usually maxima or minima.

Wavenumber (ṽ)

The reciprocal of the wavelength in centimeters, indicating the number of waves per cm in units of cm-1.

Radiant Power (P)

The amount of energy reaching a given area per second, measured in watts (W).

Intensity (I)

The radiant power per unit solid angle.

Photons

Discrete particles of energy that make up electromagnetic radiation.

Planck’s constant (h)

A constant relating the energy of a photon to its frequency (6.63 x 10-34 Js).

Electromagnetic Spectrum

Arrangement of electromagnetic radiation types by wavelength and frequency (gamma ray, X-ray, UV, Visible, IR, Microwave, Radio).

Spectroscopic Measurements

Using the interaction of radiation with matter to obtain information about a sample.

Absorption

EMR energy transferred to an absorbing molecule, causing a transition from a low energy state to a high energy state.

Emission

EMR energy transferred from an emitting molecule to space, causing a transition from a high energy state to a low energy state.

Scattering

Redirection of light with no energy transfer.

Absorption (Energy Levels)

A transition from a lower energy level to a higher energy level with energy transfer from the radiation field.

Emission (Energy Levels)

A transition from a higher energy level to a lower energy level with energy transfer to the radiation field; if no radiation is emitted, it’s nonradiative decay.

Emission Spectroscopy

A spectroscopic technique examining wavelengths of emitted photons during transitions from an excited state to a lower energy state.

Absorption Spectroscopy

Spectroscopic techniques measuring the absorption of radiation as a function of frequency or wavelength.

Chemiluminescence Spectroscopy

Spectroscopic technique involving light emission as a result of a chemical reaction.

Photoluminescence Spectroscopy

Spectroscopic techniques describing light emission from matter after photon absorption.

Transmittance (T)

The fraction of incident radiation transmitted through a sample medium (P/Po).

Absorbance (A)

A measurement of the amount of radiant power absorbed by the sample, defined as the negative log of T.

Beer’s Law

Absorbance is directly proportional to the concentration and path length. A = bc

Molar Absorptivity (ε)

The constant of proportionality in Beer's Law when concentration is expressed in mol/L and path length in cm, with units of L mol-1 cm-1

Calibration Curve

A graph plotting absorbance versus concentration

Limitations of Beer’s Law

Fundamental, chemical, and instrument deviations that cause non-linear relationships.

Instrumental Deviations

Occur due to how the absorbance measurements are made. Polychromatic and stray radiation.

Chemical Deviations

Occur when the analyte undergoes dissociation, association, or reaction with the solvent.

Atomic Absorption

Electrons bound to atoms have discrete energies; transitions between electronic levels produce line spectra.

Molecular Absorption

Molecules absorb energy by raising electrons, increasing vibration of nuclei, or increasing rotation.

Absorption Spectrum

A plot of absorbance as a function of wavelength or frequency

Emission Spectrum

A plot of the relative power of emitted radiation as a function of wavelength or frequency.

Line spectrum

A series of sharp, well-defined peaks caused by excitation of individual atoms.

Band spectrum

Several groups of lines so closely spaced that they are not completely resolved.

Continuum spectrum

A beam of light that contains a broad, smooth distribution of photon wavelength.