Chapter 16: IR Spectroscopy

Spectroscopy

The study of the interaction of electromagnetic radiation with matter

Electromagnetic Radiation

A form of energy that has characteristics of both waves and particles.

Wavelength

A distance between two successive maxima or minima in a wave’s oscillation

Frequency

The number of complete wave oscillations that occur in a given time

Planck’s Constant

The constant proportionality that appears in the dependence of a photon’s energy on its frequency 6.626 × 10 ^-34J

Infraed Spectroscopy

Study of the interaction of a sample with radiation from the infrared region of the electromagnetic spectrum, absorbance of this radiation increases the energy in molecular vibrations

Transmittance

In spectroscopy, the portion of light sent through a sample that reaches a detector

IR spectrum

A plot of %T of infrared radiation for a sample, on the Y axis, against wavenumbers, a unit of frequency on x axis

Wavenumber

A unit of frequency that is calculated by taking the reciprocal of wavelength in centimeters, that is dividing 1 by the wavelength in cm. Physically a wavenumber corresponds to the number of waves that fit in 1 cm.

Absorption Band

A feature of spectrum where absorbance is high

Strong absorption

An absorption whose transmittance is near zero

Weak absorption

An absorption whose transmittance is near 100

Stretching

The distance between two atom in a chemical bond grows longer and shorter throughout one vibrational cycle

bending

in which an angle becomes larger and smaller throughout one vibrational cycle

Symmetric stretching

Vibrational motion in which two or more bonds within a molecule stretch simultaneously and compress simultaneously

Asymmetric stretching

vibrational motion involving two bonds within a molecule, in which one bond lengthens while the other bond shortens

In-plane bending

vibrational motion of a molecule in whih bond angles change but atoms involved in the vibrations remain in the same plane

Out-of-Plane bending

Vibrational motion of a molecule in which the vibrating set of atoms occupies different planes throughout an oscillation

Fingerprint Region

Region of samples infrared spectrum below -1400cm. A fingerprint regions is often difficult to analyze but is unique to each compound

Hooke’s Law

V Spring = sq root of (k/u).

Force constant

Often thought of as spring stiffness, vibrational frequency proportional to sq root of K

Reduced mass

The quantity that relates masses of two objects connected to spring.