We report here the first measurements of the complete valence shell binding energy spectra and the frontier orbital momentum profiles of methylpropane, also known as isobutane (CH,CH(CH,)CH,), using a high-resolution binary (e, 2e) electron momentum spectrometer, at an impact energy of 1200 eV plus the binding energy and using symmetric non-coplanar kinematics. Binding energy spectra of the complete valence shell have been obtained at a coincidence energy resolution of 0.95 eV FWHM. The experimental momentum profile of the HOMO (6a(1)) and NHOMO (5e) frontier orbitals is also obtained and compared with the theoretical momentum distributions calculated using Hartree-Fock; and density functional theory (DFT) methods with various basis sets. The experimental measurements are well described by the HF and DFT calculations. (C) 1999 Elsevier Science B.V. All rights reserved.