Absolute frequency measurements of the 2-0 band of CO at 2.3 μm; Calibration standard frequencies from high resolution color center laser spectroscopy

The absolute frequencies of 20 lines of the 2-0 band of CO near 4260 cm ^-1 have been measured by heterodyne frequency measurement techniques. Eleven of the lines were measured by saturated absorption techniques which produced linewidths of about 3 MHz. New rovibrational constants have been fitted to these measurements. A table of calculated transition frequencies is given with estimated absolute uncertainties as small as 0.0000023 cm ^-1 (70 kHz) near the band center. The pressure shifts of three lines have been measured and fall in the range from -0.9 to -3 kHz/Pa (-122 to -400 kHz/Torr). It is suggested that the generally accepted frequencies of the 1-0 band of CO should be lowered by 7 MHz.