HIGHLY PRECISE WAVELENGTHS IN THE INFRARED II: HCN, $N_{2}O$ AND $CO^{*}$

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1961

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Ohio State University

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A discussion is given of the effect of mechanical errors in a grating drive on the accuracy with which line frequencies can be measured. It is shown that it is highly improbable that a mechanical device used to rotate a diffraction grating can be constructed with sufficient precision so that the line frequency error will be determined by the optical information observable in the near infrared spectrum. Making use of the echelle spectrograph 67 lines of the 001--000 absorption band of HCN have been measured. Almost 400 lines from five $N_{2}O$ absorption bands arising from the ground state of the molecule have been measured. In addition 11 lines from the 1--0 fundamental band of CO have been measured in order to determine $\nu_{0}$ for this band. In all cases only band lines have been measured which appear to be free of blends. The molecular constants for the above bands have been determined making use of the combination relationships applying least squares methods to the tables. The tables contain over 600 line frequencies. We believe the calculated like frequencies (lines free of blends) have an absolute accuracy of about 1 part in $5\times 10^{6}$ and a relative accuracy referring to lines within a given band somewhat greater.

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$^{*}$ This research was assisted by support from the Office of Naval Research and the National Science Foundation.
Author Institution: Department of Physics, The Pennsylvania State University

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