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We present Atacama Large Millimeter Array (ALMA) Cycle-0 observations of theCO J = 6-5 line in the advanced galaxy merger Arp 220. This line traces warmmolecular gas, which dominates the total CO luminosity. The CO emission fromthe two nuclei is well resolved by the 0.39" x 0.22" beam and the exceptionalsensitivity and spatial/spectral resolution reveal new complex features in themorphology and kinematics of the warm gas. The line profiles are asymmetricbetween the red and blue sides of the nuclear disks and the peak of the lineemission is offset from the peak of the continuum emission in both nuclei byabout 100 pc in the same direction. CO self-absorption is detected at thecenters of both nuclei but it is much deeper in the eastern nucleus. We alsoclearly detect strong, highly redshifted CO absorption located near thesouthwest side of each nucleus. For the eastern nucleus, we reproduce the majorline profile features with a simple kinematic model of a highly turbulent,rotating disk with a substantial line center optical depth and a large gradientin the excitation temperature. The red/blue asymmetries and line-to-continuumoffset are likely produced by absorption of the blue (SW) sides of the twonuclei by blue-shifted, foreground molecular gas; the mass of the absorber iscomparable to the nuclear warm gas mass (10^8 M_solar). We measure an unusuallyhigh L_CO/L_FIR ratio in the eastern nucleus, suggesting there is an additionalenergy source, such as mechanical energy from shocks, present in this nucleus.

Morphology and Kinematics of Warm Molecular Gas in the Nuclear Region of Arp 220 as Revealed by ALMA