The conformer II of α-alanine is approximately 240 cm^–1 or 350 K higher in energy than conformer I. This conformer has an intermolecular H bond between the H atom of the carboxyl group and the N atom of the amino group. The microwave frequencies have been reported by
(1) S. Blanco, A. Lesarri, J.C. Lòpez, and J.L. Alonso, 2004, J. Am. Chem. Soc. 126, 11675.
The millimeter wave frequencies have been reported by
(2) P. D. Godfrey, S. Firth, L. D. Hatherley, R. D. Brown and A. P. Pierlot, 1993, J. Am. Chem. Soc. 115, 9687;
and by
(3) Y. Hirata, S. Kubota, S. Watanabe, T. Momose, and K. Kawaguchi, 2008, J. Mol. Spectrosc. 251, 314.
Extrapolations are assumed to be reliable as long as the predicted uncertainties do not exceed 0.4 MHz.
The ¹⁴N hyperfine splitting was resolved in (1). It may be resolved in cold sources or at lower frequencies. Therefore, separate predictions with hyperfine splitting are provided for J up to 10. The partition function takes into account the spin multiplicity g_I = 3 of the ¹⁴N nucleus !
No vibrational state and no other conformer were considered in the calculation of the partition function. Moreover, the partition function of conformer II does NOT take into account the energy difference between conformer I and II !
The dipole moment was reported in (2).