Infrared Spectroscopy Lecture Notes

A set of flashcards based on key concepts from the lecture on Infrared Spectroscopy, covering definitions, concepts, applications, and instrumentation.

What is Infrared (IR) spectroscopy based on?

IR spectroscopy is based on IR absorption by molecules as they undergo vibrational and rotational transitions.

What are the main types of motions that molecules undergo according to IR spectroscopy?

Molecules undergo rotations, translations, and changes in bond lengths, bond angles, dihedral angles, and other types of motions.

What does the potential energy in IR spectroscopy resemble?

The potential energy resembles a classic harmonic oscillator.

What is the range of IR radiation in wavenumbers?

The range of IR radiation is 12,800 – 10 cm-1.

Why are IR spectra often sharper than UV-Vis spectra?

IR spectra are sharper because they have smaller differences in rotational transitions.

How is the vibration frequency in IR spectroscopy determined?

Vibration frequency depends on the mass of atoms and the strength of a bond.

What does the harmonic oscillator model describe?

The harmonic oscillator model describes the basic representation of atomic stretching and bonding using a spring analogy.

What must occur for a molecule to absorb IR radiation?

A vibration must occur at the same frequency as the IR light and must result in a change in the molecule's net dipole moment.

What are the types of molecular vibrations?

Types include bond stretching, bond bending, in-plane rocking, in-plane scissoring, out-of-plane wagging, and out-of-plane twisting.

What is the formula to determine the number of vibrational modes in non-linear molecules?

The number of vibrational modes is given by 3N-6 for non-linear molecules.

What is the role of the sample cell in an IR instrument?

The sample cell must be made of IR transparent material.

What is one major application of IR spectroscopy?

One major application is qualitative analysis for compound identification.

What is the Fingerprint Region in IR spectroscopy?

The Fingerprint Region (1200-700 cm-1) contains many single bond signals and is unique due to its complexity.

What is the difference in detector response between normal IR and FTIR?

FTIR offers faster response time and less noise due to the use of signal averaging.

How can modern IR instruments aid in compound identification?

They often have reference IR spectra on file that allow for matching based on the location of strongest bands.

What is the significance of Beer’s Law in quantitative analysis in IR spectroscopy?

There are deviations with Beer’s Law due to more complex spectra and limitations of IR instruments.