The effects on the vibrational spectra of placing a H-2 molecule into an electrostatic field are theoretically investigated. The field-induced infrared absorption is computed and the variation of the vibrational frequency is accounted for by studying the changes of the potential energy surface upon the action of the field. A simple model relating the field-induced infrared absorption to the charge displacement between the atoms of the H-2 molecule is proposed. (c) 2005 Elsevier B.V. All rights reserved.