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An introduction to the field of quantum chemistry and molecular spectroscopy, focusing on the fundamental concepts of light-matter interaction and various spectroscopic techniques. Topics covered include the nature of electromagnetic radiation, resonance and non-resonance interactions, and the role of spectral parameters in understanding molecular behavior. Students will gain a solid foundation in the principles of spectroscopy and its applications in chemistry.
Typology: Lecture notes
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Lecture 01: What is Spectroscopy? Lecture 02: Light-Matter Interaction Lecture 03: Spectra & Spectral Parameters 1: Spectral Broadening Lecture 04: Spectra & Spectral Parameters 2: Spectral Intensity Lecture 05: Born-Oppenheimer Approximation
Reference Texts
EMR
Harmonic wave having mutually perpendicular electric & magnetic vectors propagated from a source and travelling in straight line except when refracted or reflected.
It is produced by the oscillation of electric charge and
magnetic field residing on the atom
Features of EMR
magnetic field
Dispersion
Optical Spectroscopy
Light matter interaction involves promotion of
molecules or atoms to higher energy levels, which
already exist.
Microwave spectroscopy – Rotational
IR spectroscopy – Vibrational
UV-VIS spectroscopy - Electronic
Raman: Scattering spectroscopy
Resonance Spectroscopy
Involves creation of energy levels followed by
Light –matter interaction promotes molecules or
atoms within created energy levels
NMR spectroscopy – Radio waves
ESR/EPR spectroscopy – Microwave
How does L-M interaction happen?
Resonance interaction leads to energy absorption
Energy Absorption
Quantized Levels & Bohr conditions
∆ Erot: ∆ Evib: ∆ Eel :: 1:
3 :
6
Bohr Condition ∆E=hν
Type of Radiation
Frequency Range (Hz)
Wavelength Range
Type of Transition
gamma- rays
10 20 -10 24 <1 pm nuclear
X-rays 10 17 -10 20 1 nm-1 pm inner electron
ultraviolet 10 15 -10 17 400 nm-1 nm^ outer electron
visible 4-7.5x10 14 750 nm-400nm outer electron
near- infrared
1x10 14 -4x10 14
2.5 μm- nm
outer electron molecular vibrations
infrared 10 13 -10 14 25 μm-2.5 μm^ molecular vibrations
microwaves 3x10 11 -10 13 1 mm- μm
molecular rotations, electron spin flips* radio waves
<3x10 11 >1 mm nuclear spin flips*
Rotation & EMR
17
Vibration & EMR
19
Symmetric Stretching Vibration
Vibration & EMR
20
Bending Vibration
