We made a helium atom beam scattering (HAS) apparatus to study the thermal dynamics of adsorbed organic molecules on a surface. The apparatus had an angular resolution of 6degrees and energy resolutions of 20%, with an incident energy of E-i = 63 meV. We measured the thermal stability of acetic acid (CH3-COOH) and succinic acid (HOOC-CH2-CH2-COOH) structures on a Cu(110) using the DW-plot technique, (the temperature variation of intensity of the He beam specularly reflected from the surface). We found that the desorption temperatures derived from DW-plots are 540 K for low-coverage acetate, 550 K for c 2 x 2) acetate and 590 K at succinate. The desorption temperature of succinate is higher than acetate, which is interpreted by a larger number of carboxylates in one molecule. (C) 2004 Elsevier B.V. All rights reserved.