4448 PCHEM SET - Vibration and Rotation Spectroscopy

FTIR

Fourier transform infrared spectroscopy - an instrument that uses infrared light to collect the vibrational spectra of molecular substances, entered by DW

Raman Spectroscopy

A type of vibrational molecular spectroscopy that uses inelastic scattering of visible photons of light, entered by DW

Rule of Mutual Exclusion

In a molecule with an inversion center, symmetric molecular vibrations are seen only in Raman spectrum, while asymmetric molecular vibrations are only seen in infrared spectrum. From class notes, entered by Kyler Kelley.

Anharmonicity

The deviation of the actual vibrational potential energy away from the model harmonic potential (parabolic) energy. Atkins Physical Chemistry 11ed., page 444, entered by Aurelia Holifield, edited by DW

Electromagnetic Spectrum

The range of radiation frequencies from radio waves to gamma waves that is emitted and absorbed by various objects. From class notes, Entered by Kyler Kelley. edited by DW

Dispersive Spectrometer

The resolution of this type of instrument depends on grating, slits, source image, and number of diodes on an array detector. This type is best for kinetics because it is easier to monitor a single wavelength value over time. from class notes, entered by Ryan Goldstein, edited by DW

Interferometric Spectrometers

Uses a Michelson interferometer to give an interferogram, which a fast fourier transform converts into a spectrum. Resolution depends on max path length difference and displacement. from class notes, entered by Ryan Goldstein. edited by DW

Attenuated Total Reflectance (ATR) attachment

This sampling technique enables samples to be examined in solid or liquid state with no sample preparation. from class notes, entered by Ryan Goldstein, edited by DW

Stokes scattering

Photons in this situation lose energy to the molecules and the emerging radiation has a lower frequency or longer wavelength. Atkins, pg. 419, entered by Aurelia Holifield, edited by DW

Anti-stokes scattering

Photons in this situation gain energy from the molecules and the emerging radiation has a higher frequency or shorter wavelength. Atkins, pg. 419, entered by Aurelia Holifield, edited by DW

Harmonic oscillator

A mass on a spring (bonded atom) that has a parabolic potential energy (a restoring force proportional to the square of its displacement, V=0.5kx², from the equilibrium position).

Atkins Physical Chemistry 11ed., pg. 273 entered by Marrisa Martinez, edited by DW

Normal mode

The vibration of the molecule in which the center of mass remains fixed, the orientation is unchanged, and the atoms move synchronously. Atkins Physical Chemistry 11ed., pg. 452 entered by Marrisa Martinez

Combination bands

Simultaneous excitation of more than one normal mode in a transition Atkins Physical Chemistry 11ed., pg. 453 entered by Marrisa Martinez

Fingerprint region (related to IR spectroscopy)

The regions where all the bending vibrations (and some heavy-atom stretches) are seen in the right hand side of the spectroscopy graph, Entered by Megan Mann, edited by DW

Fourier Transform

This transformation treats the interferogram as a superposition of cosines and converts the interferogram into a spectrum of the frequencies of those cosines. Atkins Physical Chemistry 11ed., pg. 511-512 entered by Phillip Paik, edited by DW

Force constant (related to harmonic oscillator)

The harmonic potential energy curve (V = 0.5kx² is scaled by this value (k). This variable shows the strength of potential energy and is expressed in newtons per meter (N m⁻¹). Atkins Physical Chemistry 11ed., pg. 274 entered by Phillip Paik, edited by DW

Harmonic potential energy equation

V(x)=(1/2)kx² Atkins Physical Chemistry 11ed., pg. 273 entered by Phillip Paik, edited by DW

Rayleigh Scattering

Photos in this situation change direction when colliding with a molecule, but they do not lose or gain energy. there are no changes to the frequency or wave length of light.From class notes, entered by Makenzie Kuehn, edited by DW

Reduced mass

The effective mass µ that moves in the vibration or rotation of a molecule. For a diatomic molecule, µ=(m1*m2)/(m1+m2) Atkins Physical Chemistry 11th ed., pg 443, entered by Makenzie Kuehn, edited by DW

Evanescent wave

When an IR beam is reflected internally by an ATR crystal, this is the wave that penetrates a small distance into the sample ThermoFisher Scientific, Dr. Michael Bradley, entered by Makenzie Kuehn, edited by DW

Microwave Spectral Region

In this spectral region the molecule is only rotating, no vibrations. Will only effect molecules with a permanent dipole. Notes from Lecture notes, entered by Patricia Hernandez

MIR Spectral Region

400-4000 cm^-1. This region shows you the different vibrational modes of a molecule. It can tell you how a molecule is bonded together. From Lecture notes, entered by Patricia Hernandez

Dissociation energy (D subscript o)

The energy difference between the lowest vibrational state (V=0) and infinitely separated atoms. Atkins Physical Chemistry 11th ed., pg 445, entered by Breanna Nelson

Centrifugal Distortion Constant

Dj - a measure of the distortion of the bond length of a molecule as the angular momentum, or rotation, increases. Bonds that are easily stretched have lower vibrational energies, weaker force constants, and thus high centrifugal distortion. Atkins Physical Chemistry 11th ed, pg 434, entered by Taylor Shelley, edited by DW

Rotation-vibration Coupling Constant

ae (alpha-e) - a measure of how the change in internuclear distance of a bond during vibration affects the moment of inertia and therefore the rotation of the molecule. From Nibler Exp #37 Handout from the Rovibrational spectroscopy lab, entered by Taylor Shelley

Rotational Constant

Be - a measure of how the moment of inertia and bond length affect the energy of rotation. Heavier molecules have larger moments of inertia, so they have smaller transition energies and closely spaced rotational energy levels. Atkins Physical Chemistry 11th ed, page 432, entered by Taylor Shelley

Polarizability

A measure of the ability of an electric field to induce a dipole moment in a molecule. Atkins Physical Chemistry 11th ed, page 592, entered by Marrisa Martinez

Permanent dipole moment

The partial charges on the atoms in the molecule, which arise from differences in electronegativity or variations in electron density through the molecule. Atkins Physical Chemistry 11th ed, page 585, entered by Marrisa Martinez

P branch

A spectral branch in vibration-rotation spectra that consists of all transitions with ΔJ = -1. This branch consists of lines extending to the low wavenumber side of the spectrum. Atkins Physical Chemistry 11th ed, page 447, entered by Marrisa Martinez, edited by DW

Raman Shift

Using visible light to measure vibrational properties in the Mid-IR energy range. From lecture notes L17. Entered by Breanna Nelson

R branch

A spectral branch in vibration-rotation spectra that consists of all transitions with ΔJ = +1. This branch consists of lines extending to the high wavenumber side of the spectrum. Atkins Physical Chemistry 11th ed, page 447, entered by Marrisa Martinez, edited by DW

Q branch

A spectral branch in vibration-rotation spectra that consists of all transitions with ΔJ = 0. This branch consists of lines that fall on the vibrational frequency. Entered by DW

S branch

A spectral branch in vibration-rotation spectra that consists of all transitions with ΔJ = +2. This branch consists of lines extending to the high wavenumber side of the spectrum. Entered by DW

O branch

A spectral branch in vibration-rotation spectra that consists of all transitions with ΔJ = -2. This branch consists of lines extending to the low wavenumber side of the spectrum. Entered by DW