Rovibronic Infrared Spectrum of a Rigid Diatomic Rotor
Rovibronic Infrared Spectrum of a Rigid Diatomic Rotor
This Demonstration lets you study rotationally-resolved infrared band spectra of the vibrational transition in diatomic molecules. Due to quantized vibrational and rotational energy levels and the selection rules and , allowed transitions result in a highly ordered spectrum consisting of a P branch ( , smaller wavenumbers) and an R branch ( , larger wavenumbers) separated by a central gap. Adjacent spectral lines are separated by a spacing of , and since line intensities depend on the Boltzmann factor for thermal population and the quantum number , each branch monotonically increases and/or decreases. As temperature increases, more lines are observed and the intensities of the lines decrease due to the population being spread over more rotational levels. Interactivity involves the effects of the fundamental vibrational frequency, rotational constant , temperature, and line width on the observed spectrum.
v
0
v
1
Δv=±1
ΔJ=±1
ΔJ=-1
ΔJ=+1
2B
J
B