Fundamentals of Molecular Physics

This book starts with the introduction to quantization of molecular energies, rotational energy spectra, vibrational energy spectra, electronic transition spectra and quantized energies or discrete set of energies of a molecule. Quantized rotational energy levels of molecules has been discussed in case of pure rotational Spectra (case of rigid diatomic molecule - rigid rotator). Consequently, the rotational quantum number, rotational constant of the molecule and the transition rule also has been discussed. Minimum energy for the excitation of rotational energy level of molecule, transition rule for pure rotational spectra, wave number and wavelength of spectral line for successive rotational energy transition, difference in frequencies and difference in wave numbers (common wave number interval) are also discussed. By knowing the common wave number interval from molecule's rotational spectrum and by calculating the reduced mass, the calculation of rotational constant, moment of Inertia and internuclear distance of heteronuclear diatomic molecules such as have been studied. Intensity of rotational spectral lines at rotational energy level on the molecular spectra and the molecular population density at that level also has been studied. Later on, quantized vibrational energies of a molecule, its pure vibrational Spectra, reduced Mass, frequency of vibration and vibrational energy gap of molecule, transition rule for pure vibrational spectra, wavenumber and wavelength of vibrational spectral line have been discussed. For the diatomic molecule, concepts of rigid rotator and non-rigid rotator have been studied with the types of molecules based on moment of inertia. The study has been elongated with discussion on rotational vibrational spectra (V-R Spectra), transition rules for V-R spectra, frequency of radiation in V-R emission Spectra, R-branch and P-branch on V-R spectra, Born-Oppenheimer approximation, diatomic molecule as a harmonic oscillator, i.e. harmonically vibrating diatomic molecule, equation of S. H. M. for diatomic harmonic oscillator, its frequency and wave number, energy levels of diatomic harmonic oscillator, molecule as an anharmonic oscillator, i.e. anharmonic vibrating diatomic molecule. The study has been ended with short discussion on fundamental and overtone frequencies, and dissociation energy.