Anti and gauche conformers have been identified for gas-phase benzenepropanenitrile (BPN) using one-colour resonant two-photon ionisation (R2PI) spectroscopy. Conformational assignments were based on rotational band contour analysis supported by ab initio calculations. The anti conformer origin shows a pure b-type rotational contour, whilst the gauche conformer origin exhibits a hybrid band with largely a-type character, resulting from significant rotation in the transition dipole moment. A slight energetic preference for the gauche conformer is observed. The spectrum of the BPN(H2O)(1) water complex has also been measured, and a structure in which water acts as a proton donor inferred. (c) 2006 Elsevier B.V. All rights reserved.