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We present the first broadband lambda = 1 mm spectrum toward the z=2.56Cloverleaf Quasar, obtained with Z-Spec, a 1-mm grating spectrograph on the10.4-meter Caltech Submillimeter Observatory. The 190-305 GHz observation bandcorresponds to rest-frame 272 to 444 microns, and we measure the dust continuumas well as all four transitions of carbon monoxide (CO) lying in this range.The power-law dust emission, F_nu = 14 mJy (nu/240GHz)^3.9 is consistent withthe published continuum measurements. The CO J=6->5, J=8->7, and J=9->8measurements are the first, and now provide the highest-J CO information inthis source. Our measured CO intensities are very close to thepreviously-published interferometric measurements of J=7->6, and we use allavailable transitions and our 13CO upper limits to constrain the physicalconditions in the Cloverleaf molecular gas disk. We find a large mass(2-50x10^9 Msun) of highly-excited gas with thermal pressure nT > 10^6 Kcm^-3.The ratio of the total CO cooling to the far-IR dust emission exceeds that inthe local dusty galaxies, and we investigate the potential heating sources forthis bulk of warm molecular gas. We conclude that both UV photons and X-rayslikely contribute, and discuss implications for a top-heavy stellar initialmass function arising in the X-ray-irradiated starburst. Finally we presenttentative identifications of other species in the spectrum, including apossible detection of the H20 2_0,2->1_1,1 transition at lambda_rest = 303microns.

The Warm Molecular Gas Around the Cloverleaf Quasar