Variation of Fundamental Constants as Revealed by Molecules: Astrophysical Observations and Laboratory Experiments

In this chapter, we describe the application of precision molecular spectroscopy to the study of a possible temporal and spatial variation of the fundamental constants.As we will show below, molecular spectra are mostly sensitive to two such dimensionless constants, namely the fine-structure constant α = e2/c and the electron-to-proton mass ratio μ = me/mp (note that some authors define μ as an inverse value, i.e., the proton-to-electron mass ratio). At present, NIST lists the following values of these constants [1]: α−1 = 137.035999679(94) and μ−1 = 1836.15267247(80).