Atomic and Molecular Physics: Structure & Spectra

• Atomic and molecular physics is the study of atoms as isolated systems of electrons and nuclei, and molecules as systems of atoms
• It deals with the structure, properties, behavior, and interactions of atoms and molecules

Atomic Structure

• Atoms consist of a positively charged nucleus surrounded by negatively charged electrons
• The nucleus contains protons and neutrons
• The number of protons determines the element
• The number of neutrons determines the isotope
• Electrons occupy discrete energy levels or orbitals around the nucleus
• These energy levels are quantized, meaning that electrons can only exist at specific energy values
• The electronic configuration of an atom describes the arrangement of electrons in different energy levels and orbitals
• The electronic configuration determines the chemical properties of an atom
• Hund's rule states that electrons will individually occupy each orbital within a subshell before doubling up in any one orbital

Atomic Spectra

• Atomic spectra are produced when atoms absorb or emit electromagnetic radiation
• Absorption spectra are produced when atoms absorb radiation and electrons move to higher energy levels
• Emission spectra are produced when atoms emit radiation and electrons move to lower energy levels
• The wavelengths of the spectral lines are related to the energy differences between the energy levels
• Atomic spectra are unique to each element and can be used to identify the elements present in a sample
• Selection rules govern which transitions between energy levels are allowed
• The intensity of spectral lines is proportional to the probability of the transition occurring

Molecular Structure

• Molecules are formed when two or more atoms are bonded together by chemical bonds
• Chemical bonds are formed by the sharing or transfer of electrons between atoms
• The shape of a molecule is determined by the arrangement of atoms and the types of bonds between them
• Molecular structure can be described by bond lengths, bond angles, and dihedral angles
• Molecular structure determines the physical and chemical properties of a molecule

Molecular Spectra

• Molecules can absorb or emit electromagnetic radiation, producing molecular spectra
• Molecular spectra are more complex than atomic spectra because molecules can vibrate and rotate
• Vibrational spectra arise from transitions between different vibrational energy levels
• Rotational spectra arise from transitions between different rotational energy levels
• Electronic spectra arise from transitions between different electronic energy levels
• Molecular spectra can be used to study the structure, dynamics, and properties of molecules

Spectroscopic Techniques

• Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine the concentration of an element in a sample, based on absorption of light by free metallic ions
• Atomic Emission Spectroscopy (AES) is an analytical technique used to determine the concentration of an element in a sample, based on emission of light by excited atoms
• UV-Vis Spectroscopy measures the absorption and transmission of ultraviolet and visible light by a substance
• Infrared Spectroscopy (IR) measures the absorption of infrared radiation by a substance, which provides information about the vibrational modes of the molecule
• Raman Spectroscopy measures the scattering of light by a substance, which provides information about the vibrational modes of the molecule
• Nuclear Magnetic Resonance (NMR) Spectroscopy measures the absorption of radiofrequency radiation by atomic nuclei in a magnetic field, which provides information about the structure and dynamics of molecules
• Electron Spin Resonance (ESR) Spectroscopy measures the absorption of microwave radiation by unpaired electrons in a magnetic field, which provides information about the electronic structure of molecules

Lasers

• Lasers are devices that produce coherent, monochromatic, and highly directional beams of light
• Laser operation is based on the principle of stimulated emission
• Population inversion is required for laser action to occur
• Common types of lasers include gas lasers, solid-state lasers, and semiconductor lasers
• Lasers have a wide range of applications in science, technology, and medicine

Applications of Atomic and Molecular Physics

• Atomic and molecular physics has a wide range of applications in various fields
• Spectroscopy is used in analytical chemistry, environmental monitoring, and materials science
• Lasers are used in telecommunications, manufacturing, and medicine
• Atomic clocks are used for precise timekeeping and navigation
• Plasma physics is used in fusion energy research and materials processing
• Quantum computing is a rapidly developing field that utilizes the principles of atomic and molecular physics to perform computations