An unknown gaseous sample exhibits absorption bands at 580 nm, 3.0 μm
CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
An unknown gaseous sample exhibits absorption bands at 580 nm, 3.0 μm, and 0.90 mm. Which of the following best explains why the 580 nm band is assigned to an electronic transition rather than a vibrational or rotational transition?
(a) Because 580 nm lies in the microwave part of the spectrum, transitions observed there are generally electronic.
(b) Photons at 580 nm have enough energy to excite electrons, whereas vibrational and rotational transitions usually absorb the lower–energy IR and microwave photons.
(c) Electronic transitions involve lower-energy (longer-wavelength) light than vibrational transitions; since 580 nm has less energy than 3.0 µm, it is therefore electronic.
(d) The energy of a 580 nm photon matches typical vibrational level spacings in molecules, so the band is most likely vibrational rather than rotational or electronic.