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We have compared the TeV gamma-rays with the new 12CO J=2-1 data toward HESSJ1745-303 in the Galactic center and confirmed that the molecular gasMG358.9-0.5 toward (l, b)=(358.9, -0.5 at VLSR=-100-0 km s-1 shows a reasonablepositional agreement with the primary peak (northern part) of the gamma-raysource. For the southern part of HESS J1745-303, we see no CO counterpart,whereas the HI gas in the Parkes 21 cm HI dataset shows a possible counterpartto the gamma-ray source. This HI gas may be optically thick as supported by theHI line shape similar to the optically thick 12CO. We estimate the total massof interstellar protons including both the molecular and atomic gas to be2x10^6 Mo and the cosmic-ray proton energy to be 6x10^{48} ergs in the hadronicscenario. We discuss possible origins of the cosmic-ray protons including thenearby SNR G359.1-0.5. The SNR may be able to explain the northern gamma-raysource but the southern source seems to be too far to be energized by the SNR.As an alternative, we argue that the second-order Fermi acceleration in theinter-clump space surrounded by randomly moving high-velocity clumps may offera possible mechanism to accelerate protons. The large turbulent motion withvelocity dispersion of ~15 km s-1 has energy density two orders of magnitudehigher than in the solar vicinity and is viable as the energy source.

Molecular and Atomic Gas toward HESS J1745-303 in the Galactic Center: Further Support for the Hadronic Scenario