Millimeter-wave spectroscopy of α-alanine

Millimeter-wave spectroscopy of α-alanine was carried out by using continuous molecular beam. The sample of α-alanine was heated up to 200-210 °C, and flowed with Ar buffer gas through a nozzle with a 0.4 mm diameter. Fifty-five lines of conformer I and 35 lines of conformer IIa of α-alanine were newly measured in 80-99 and 160-180 GHz regions. A least-squares analysis of the presently observed transitions combined with the previously observed millimeter-wave data below 72 GHz and Fourier transform microwave data gave a set of improved molecular constants which are useful for prediction of the transition frequencies in high frequency region. The rotational temperature of conformer I in the continuous molecular beam was estimated to be 29.9 ± 6.5 K.