High-precision laser spectroscopy of the CO A${}^1\hat{I}$ - X${}^1\hat{I}{\pounds }^{+}$ (2,0), (3,0) and (4,0) bands

Abstract

High-precision two-photon Doppler-free frequency measurements have been performed on the CO A${}^1\hat{I}$ - X${}^1\hat{I}{\pounds }^{+}$ fourth-positive system (2,0), (3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for rotational quantum numbers up to $J=5$, have been determined at an accuracy of $1.6\times 10^{-3}$ cm${}^{-1}$, using advanced techniques of two-color 2+1' resonance-enhanced multi-photon ionization, Sagnac interferometry, frequency-chirp analysis on the laser pulses, and correction for AC-Stark shifts. The accurate transition frequencies of the CO A${}^1\hat{I}$ - X${}^1\hat{I}{\pounds }^{+}$ system are of relevance for comparison with astronomical data in the search for possible drifts of fundamental constants in the early universe. The present accuracies in laboratory wavelengths of $\hat{I}”\hat{I}»/\hat{I}»=2\times 10^{-8}$ may be considered exact for the purpose of such comparisons.

13 pages, 6 figures, The Journal of Chemical Physics (2015) accepted