Energy Units and Molecular Spectra

Hereafter, we will consider only the former since topics discussed in this book do not involve magnetic phenomena. The electric field strength (E) at a given time (0 is expressed by 

The distance between two points of the same phase in successive waves is called the wavelength, X, which is measured in units such as A (angstrom), nm (nanometer), mpi (millimicron), and cm (centimeter). The relationships between these units are  

The frequency, v, is the number of waves in the distance light travels in one second. Thus, 

The third parameter, which is most common to vibrational spectroscopy, is the wavenumber, v, defined by 

As shown earlier, the wavenumber (v) and frequency (v) are different parameters, yet these two terms are often used interchangeably. Thus, an expression such as frequency shift of 30 cm-1 is used conventionally by IR and Raman spectroscopists and we will follow this convention through this book. 

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