The overall decomposition of the IR spectrum of neu-ω2=1150 cm -1 ω3=1200 cm -1 ω12=1706 cm -1 ω8=1486 cm -1 FIG. . Effective modes associated to the spectral region 1000-1800 cm -1 of the IR spectrum of neutral alanine in the gas phase, responsible for the major differences with the IR spectrum of zwitterionic alanine in the gas phase. in the spectral region 1000-2000 cm -1 for the neutral form of gas phase alanine. 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). Right column: theoretical effective frequencies from this work.