Accurate absolute reference frequencies from 1511 to 1545 nm of the ν1+ν3 band of ^12C2H2 determined with laser frequency comb interval measurements

Absolute frequency measurements, with uncertainties as low as 2 kHz (1×10−11), are presented for the ν1+ν3 band of 12C2H2 at 1.5 μm (194-198 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line of 13C2H2 and a system stabilized to the line in 12C2H2 whose frequency was to be determined, a Cr:YAG laser-based frequency comb was employed to measure the frequency intervals. The systematic uncertainty is notably reduced relative to that of previous studies, and the region of measured lines has been extended. Improved molecular constants are obtained.