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It is an open question why the temperature of molecular gas in the Galacticcenter region is higher than that of dust. To address this problem, we madesimultaneous observations in the NH_3 (J,K) = (1,1), (2,2), and (3,3) lines ofthe central molecular zone (CMZ) using the Kagoshima 6 m telescope. Theortho-to-para ratio of NH_3 molecules in the CMZ is 1.5--3.5 at most observedarea. This ratio is higher than the statistical equilibrium value, and suggeststhat the formation temperature of NH_3 is 11--20 K. This temperature is similarto the dust temperature estimated from the submillimeter and infraredcontinuum. This result suggests that the NH_3 molecules in the CMZ wereproduced on dust grains with the currently observed temperature (11--20 K), andthey were released into the gas phase by supernova shocks or collisions of dustparticles. The discrepancy between warm molecular gas and cold dust can beexplained by the transient heating of the interstellar media in the CMZapproximately 10^5 years ago when the NH_3 molecules were released from thedust.

NH3 in the Galactic Center is formed in Cool Conditions