A systematic sequential procedure is implemented to find local minimum conformers corresponding to the lowest generation (GO), -NH2- and -OH-terminated, poly(amidoamine) (PAMAM) dendrimers, and their IR vibrational spectra using ab initio (Hartree-Fock and density functional theory) techniques. It is found that the most stable conformations of PAMAM-GO dendrimers in the gas phase have all their secondary amide groups in the trans conformation. Interbranch interactions including intramolecular H-bonds play a definite role in providing structural stability. The calculated electronic density spatial distribution reveals the existence of three regions where appropriate environments would attract either an ion or a metal atom: the core, the amide, and the terminal group (NH2 or OH) sites. A detailed analysis of the IR spectra for the lowest energy conformers of PAMAM-NH2 and PAMAM-OH is thoroughly analyzed and compared with experimental data when available.