Infrared and Raman Basics

<p>Near IR (nIR) and Mid IR (B)</p> Signup and view all the answers

<p>It lacks a dipole moment change (C)</p> Signup and view all the answers

<p>~10 to 30 μm (B)</p> Signup and view all the answers

<p>Asymmetric stretching (C)</p> Signup and view all the answers

<p>Higher temperature results in shorter wavelengths (A)</p> Signup and view all the answers

<p>C-O (A)</p> Signup and view all the answers

<p>The electronegativity of the atoms (D)</p> Signup and view all the answers

<p>H2 (D)</p> Signup and view all the answers

<p>Absorption occurs if dipole moment changes during vibration (D)</p> Signup and view all the answers

<p>Molecules must have a changing dipole moment to be IR active (C)</p> Signup and view all the answers

<p>Alterations in vibrational frequencies due to changes in mass (A)</p> Signup and view all the answers

<p>The bond must have a considerable bond length (B)</p> Signup and view all the answers

<p>Number of vibrations and symmetry of the molecule (D)</p> Signup and view all the answers

<p>Amide I band (D)</p> Signup and view all the answers

<p>Strength of the hydrogen bond (D)</p> Signup and view all the answers

<p>Mid IR region (D)</p> Signup and view all the answers

<p>α-helices (C)</p> Signup and view all the answers

<p>Unique molecular identification (D)</p> Signup and view all the answers

<p>C=O and N-H bonds (D)</p> Signup and view all the answers

<p>The distribution of populations among energy levels (B)</p> Signup and view all the answers

<p>Some vibrations are much weaker than others (B)</p> Signup and view all the answers

<p>It falls within the IR spectrum. (D)</p> Signup and view all the answers

<p>The population in higher energy levels increases (C)</p> Signup and view all the answers

<p>Forensic science and biomolecule classification (A)</p> Signup and view all the answers

<p>It includes a wider range of molecular vibrations. (C)</p> Signup and view all the answers

<p>ΔE (A)</p> Signup and view all the answers

<p>Ndown decreases (A)</p> Signup and view all the answers

<p>Different samples may have similar IR spectra. (C)</p> Signup and view all the answers

<p>N is independent of k_B (B)</p> Signup and view all the answers

<p>The presence of specific molecular bonds. (D)</p> Signup and view all the answers

<p>2 (C)</p> Signup and view all the answers

<p>They can be broad and tend to overlap. (B)</p> Signup and view all the answers

<p>Tyrosine, Phenylalanine, Tryptophan. (A)</p> Signup and view all the answers

<p>Most are in the ground state (B)</p> Signup and view all the answers

<p>Multiple vibrational modes even in simple molecules. (D)</p> Signup and view all the answers

<p>More systems are likely to be in excited states (D)</p> Signup and view all the answers

<p>It is less sensitive than UV-Visible spectroscopy. (A)</p> Signup and view all the answers

<p>Tendency to be distorted (A)</p> Signup and view all the answers

<p>IR depends on electronegativity differences, while Raman relies on polarizability. (B)</p> Signup and view all the answers

<p>Because it has a large dipole moment (C)</p> Signup and view all the answers

<p>Water's Raman spectrum is weak due to low polarizability. (C)</p> Signup and view all the answers

<p>They are complementary techniques that can reveal different information about a sample. (A)</p> Signup and view all the answers

<p>The electronegativity difference between its atoms (C)</p> Signup and view all the answers

<p>It has a very low scattering ability. (D)</p> Signup and view all the answers

<p>They are always identical. (D)</p> Signup and view all the answers

IR absorption occurs only when a molecule's dipole moment changes during vibration.

The product of bond distance and charge difference between bonded atoms.

Bonds with atoms of different electronegativities (like C-O, N-O, N-H, C-H) absorb IR light.

Molecules like H2, N2, and O2 do not absorb IR light because they have zero dipole moment change during vibration.

The study of how molecules absorb and emit infrared light, related to atomic vibrations around bonds.

The process where a molecule absorbs infrared radiation, causing vibrations in bonds.

A technique used to study how molecules absorb and scatter light (especially near infrared or visible), providing a different view than IR Spectroscopy

The frequency of vibration a molecule that causes a particular bond to oscillate or vibrate.

Describes the distribution of populations among energy levels in a system.

Different possible energy states a system can occupy.

The number of systems occupying each energy level.

Constant used to calculate population probabilities at different temperatures.

Measure of the average kinetic energy of particles in a system.

Difference in energy between different energy levels.

The number of systems in each energy level.

Defines the probability of populating a particular energy level at a given temperature

Certain molecular vibrations don't show up in infrared (IR) spectra because the molecule's symmetry prevents a change in dipole moment during the vibration.

A type of molecular vibration where atoms move in and out symmetrically along a bond axis, resulting in no change in the molecule's dipole moment.

A type of molecular vibration where atoms move in and out unequally along a bond axis, resulting in a change in the molecule's dipole moment.

Electromagnetic radiation with wavelengths longer than visible light, but shorter than microwaves.

Analysis of the interaction of a material with infrared light, often used to determine molecular structure through vibrations.

Sections of the infrared spectrum most useful for biologists.

The process by which objects emit infrared radiation due to their temperature.

The unit used to measure the frequency of infrared radiation absorbed by molecules in IR spectroscopy. It represents the number of wavelengths per centimeter.

Unique patterns in IR spectra that allow for the identification of specific molecules.

The mid-infrared (mid-IR) region is most useful for identifying biological molecules like proteins, carbohydrates, lipids, and nucleic acids.

The region of the IR spectrum between 1500 cm⁻¹ and 500 cm⁻¹ that contains complex and unique absorption patterns for different molecules. It is like a fingerprint that identifies a specific molecule.

Proteins have complex IR spectra due to the numerous modes of vibration present. However, some vibrations are more intense than others.

The portion of the infrared spectrum typically used in IR spectroscopy, ranging from 4000 cm⁻¹ to 400 cm⁻¹.

The most important diagnostic band for proteins, originating primarily from the C=O stretching vibration in peptide bonds.

IR spectroscopy identifies different molecules based on the unique way they absorb infrared light. The specific vibrational modes of bonds within a molecule determine its IR spectrum.

The UV-Vis spectrum provides information about electronic transitions (electrons moving between energy levels), while the IR spectrum reveals vibrational transitions (bonds stretching and bending) within a molecule.

The frequency of the amide I band changes depending on the secondary structure of a protein.

Molecules have multiple ways to vibrate, leading to complex IR spectra. Even simple molecules have multiple vibrational modes, contributing to a multitude of absorption peaks.

The strength of the hydrogen bond between C=O and N-H groups in peptide bonds influences the amide I frequency, which is different for alpha-helices and beta-sheets.

IR spectra can distinguish between molecules with similar structures but different functional groups. The fingerprint region is especially helpful in identifying molecules with unique patterns.

Changes in the amide I band frequency can be used to study and monitor changes in protein secondary structure.

IR spectra of mixtures show the combined absorption patterns of all components. However, overlapping peaks can make it challenging to analyze individual components.

IR spectroscopy is used in various fields including diagnostics, forensic science, and cell and tissue classification due to its ability to identify unique molecular fingerprints.

The tendency of an electron cloud to distort when an electric field is applied, causing temporary dipoles.

A technique that measures how molecules scatter light to reveal information about their vibrational modes.

Bonds with high polarizability, meaning their electron cloud easily distorts during vibration, resulting in strong Raman signals.

IR spectroscopy measures how molecules absorb infrared light based on changing dipole moments, while Raman spectroscopy measures how molecules scatter light based on changing polarizability.

Water strongly absorbs IR light due to its large dipole moment, making it difficult to study other molecules in IR. However, water is a weak Raman scatterer, making it a good solvent for Raman spectroscopy.

IR and Raman spectroscopy are complementary because they focus on different properties of molecules, providing a more complete picture of their structure and dynamics.

Different ways a molecule can vibrate, each with a specific frequency and energy level.

IR and Raman spectra often look similar because vibrational modes influence both techniques, but the intensity and presence of certain peaks can differ due to the different underlying properties they measure.