In this chapter we discuss the measurement of the vibrational absorption spectrum and the vibrational circular dichroism (VCD) spectrum of a solution of a chiral solute in an achiral solvent.
The vibrational absorption spectrum of a solution is measured as follows. A cell of pathlength ℓ (cm) is lled with the solution and placed in an IR absorption spectrometer between the IR light source, S, and the IR detector, D:
The absorption of the solution causes the intensity of the light of frequency ν entering the cell, I0(ν), to be reduced to I(ν). The transmittance T and the absorbance A of the solution at frequency ν are dened by:
I ( )
( ) ( )
0 A T( ) log ( )ν ν= − 10
If T = 10-1, i.e., 90% of the light is absorbed, A = 1. The intensities I and I0 are measured by the detector with the cell inside and outside the spectrometer, respectively. The IR absorption spectrometer measures T and A over a range of frequencies, generating the vibrational absorption spectrum of the solution, now termed the IR absorption spectrum.