Improved Laboratory Values of the H-2 Lyman and Werner Lines for Constraining Time Variation of the Proton-to-Electron Mass Ratio

Two distinct high-accuracy laboratory spectroscopic investigations of the H2 molecule are reported. Anchor lines in the EFΣg+1-XΣg+1 system are calibrated by two-photon deep-UV Doppler-free spectroscopy, while independent Fourier-transform spectroscopic measurements are performed that yield accurate spacings in the BΣu+1-EFΣg+1 and IΠg1-CΠu1 systems. From combination differences accurate transition wavelengths for the B-X Lyman and the C-X Werner lines can be determined with accuracies better than ∼5×10-9, representing a major improvement over existing values. This metrology provides a practically exact database to extract a possible variation of the proton-to-electron mass ratio based on H2 lines in high-redshift objects. Moreover, it forms a rationale for equipping a future class of telescopes, carrying 30-40 m dishes, with novel spectrometers of higher resolving powers. © 2008 The American Physical Society.