Knowledge Bank

The microwave spectrum of piperidine, $CH2CH2CH2CH2CH2NH$, has been examined in detail between 18000 and 32000 Mc/sec. The species producing the most prominent transitions (both Q-branch and R-branch with an a-axis transition dipole moment) has rotational constants $A=4494.6,B=4395.2C=2535.6$ Mc/sec. These are in good agreement with calculated rotational constants, assuming reasonable values for bond lengths and angles, with the molecule in the chair form'' and the amino-hydrogen in the equatorial'' position. Many satellite lines are attributable to transitions in excited vibrational states. However, there remains many strong lines which must arise from transitions between two different sets of rotational levels displaced by a few thousand megacycles. The possible identification of the two sets as inversion levels of a non-rigid molecular species will be discussed.