ISOTOPE EFFECTS
The different isotopes in a particular species may give fine detail in infrared spectroscopy. For example, the O-O stretching frequency of oxyhemocyanin is experimentally determined to be 832 and 788 cm−1 for ν(16O-16O) and ν(18O-18O) respectively.
By considering the O-O as a spring, the wave number of absorbance, ν can be calculated.
where c is the speed of light, k is the spring constant for the bond, and μ is the reduced mass of the A-B system.
The reduced masses for 16O-16O and 18O-18O can be approximated as 8 and 9 respectively. So,
TWO DIMENSIONAL IR SPECTROSCOPY (2DIR)
Two-dimensional infrared spectroscopy is a nonlinear infrared spectroscopy technique that has the ability to correlate vibrational modes in condensed-phase systems.
This technique provides information beyond linear infrared spectra, by spreading the vibrational information along multiple axes, yielding a frequency correlation spectrum.
Experiments of two-dimensional infrared spectroscopy have only become possible with the development of ultra fast lasers and the ability to generate femtosecond infrared pulses.
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