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We have detected the 12CO J=12-11 and J=14-13 lines (at 1382 and 1612 GHz, respectively) in selected regions of the molecular cloud complexes W3, W51, M17, DR21, and W49. More recently the J=16-15 line at 1841 GHz was observed in all sources except W49. The data were obtained with a laser heterodyne spectrometer flown aboard NASA's Kuiper Airborne Observatory. Measurements of these lines at 0.6 km/s resolution allow us to distinguish between UV- and shock-heating mechanisms for the high-excitation gas. The high-J linewidths lie in the range of 4-20 km/s (FWHM), similar to those for low-J (J<4) CO emission in these sources. This correspondence suggests that the hotter gas (T = 200-500 K) is dynamically linked to the quiescent gas component, perhaps by association with the UV-heated peripheries of the numerous cloud clumps. None of these sources show any high-J evidence for shock-excitation (i.e., linewidths > 30 km/s), in contradiction to some previous reports. This work was supported by NASA Grants NAG2-254 and NAG2-753.
