Communication: Molecular near-infrared transitions determined with sub-kHz accuracy

Precise molecular transition frequencies are needed in various studies including the test of fundamental physics. Two well isolated ro-vibrational transitions of (CO)-C-12-O-16 at 1.57 mu m, R(9) and R(10) in the second overtone band, were measured by a comb-locked cavity ring-down spectrometer. Despite the weakness of the lines (Einstein coefficient A similar or equal to 0.008 s(-1)), Lamb-dip spectra were recorded with a signal-to-noise ratio over 1000, and the line positions were determined to be 191 360 212 761.1 and 191 440 612 662.2 kHz, respectively, with an uncertainty of 0.5 kHz (delta nu/nu = 2.6 x 10(-12)). The present work demonstrates the possibility to explore extensive molecular lines in the near-infrared with sub-kHz accuracy. Published by AIP Publishing.