The translational and orientation order of arg-cysteamine molecules chemiabsorbed on the Au(111) crystal surface is considered. Couplings between carbon, nitrogen, and hydrogen atoms of the n-alkanethiols are approximated by the Lennard-Jones potential. Moreover, hydrogen bonds between oxygen and nitrogen and dipole-dipole interactions of the dipole moments of different atomic groups are taken into account. It is found that molecules are arranged in a 2x2 lattice and have the total symmetry C(6)xZ(2). The critical temperature of the phase transition to the tilted state T-c1, which breaks the symmetry C-6, is estimated to be extremely high. The spontaneous breakdown of the remaining symmetry Z(2) leads to the twisted state of the molecules and has the critical temperature T-c2=340 K. (C) 2004 American Institute of Physics.