In the paper we have constructed and investigated some properties of the Perelomov's "generalized coherent states" and photon-added coherent states for the Morse onedimensional Hamiltonian (MO-PACSs), using the SU(2) group generators. We have found the integration measure in the resolution of unity and we have calculated some expectation values in the MO-PACSs representation. Using these states, the diagonal P-representation of the density operator is constructed as a new result for Morse potential. In addition, we have calculated some thermal expectation values for the quantum canonical diatomic gas of the Morse oscillators.PACS : 03.65. Ca, 31.15.Hz,