A diatomic gas displays spectral lines corresponding to transitions separated by about 0.4cm−1 (wavenumber). Which type of electromagnetic radiation would most effectively induce these transitions?
a) Radio-frequency radiation with wavelengths on the order of 3m
b) Microwave radiation with wavelengths on the order of a few centimeters
c) Mid-infrared radiation with wavelengths near 4μm
d) Millimetre-wave radiation with wavelengths of about 4mm