Author Institution: Los Alamos Scientific Laboratory, University of CaliforniaTwenty-two spectral lines of the 13C16O2β Q-branch at 617cmβ1 have been observed, and fitted by a cubic polynomial in J(J+1) to a standard deviation of Β±Β 3Γ10β4cmβ1. Another Q-branch, at 630.7cmβ1, has been observed for 12 lines, and fitted to a linear polynomial in J(J+1) to Β±Β 9Γ10β4cmβ1. The resulting molecular constants are given in Table I. [FIGURE] In addition, the positions of several lines from other isotopes and other bands have been measured with great accuracy relative to the adjacent lines of the above Q-branches