Near-infrared (NIR) spectra of acetic acid in a low-temperature argon matrix were measured in the range of 3950-12000 cm(-1), where approximate to 40 sharp combination and overtone bands were observed and assigned. The first and second overtone bands for the OH stretching mode, assigned by use of the observed H-D isotope shifts and density functional theory calculations at the B3LYP/631++G** level. The observed wavenumbers were essentially reproduced by the anharmonic wavenumbers estimated by the GAUSSIAN 03 program extended to the NIR region. (c) 2005 Elsevier B.V. All rights reserved.