Knowledge Bank

The 2 -- 0 band lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O$, at about $4260cm-1$, are the most frequently used ones for the wavenumber calibration of near infrared spectrometers. The values of these wavenumbers, up to now considered as standards, have been given a long time ago by D.H. Rank and his co-workers$.1$ The High Information Fourier Spectrometer, built at Laboratoire AIME COTTON, is now operating in $Vacuum2$ and provides absolute wavenumber measurements. It has been used to measure the 2 - 0 band of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O,$ which lines were directly referred, in the experiment, to the Krypton 86 Standard line at 16 $507.6373cm-1$. The estimated relative error on the lines position is $3\times 10-8$. The relative precision is increased by 16 when compared with that of the previous standards. Comparison between the two sets of CO lines shows some discrepancies. The $B0$ rotational $constant3$ leads, combined with the $B0$ value given by P. Heminger $etal4$ leads to the following Velocity of Light $c=299792.46(\pm 0.070)$ km/s. The precision on the i.r. and the r.f. $B0$ rotational constant values have the same order of magnitude.