the region 1500-1600 cm -1 and are mainly produced by in the spectral region 1000-2000 cm -1 for the zwitterionic form of alanine in the gas phase. Central column: bands assignment using the abbreviation from Ref. (ρ for rocking, δ for bending, ν for stretching, ω for wagging; s for symmetric and as for asymmetric modes). Right column: calculated effective frequencies from this work.