ROTATION-VIBRATION CONSTANTS OF AMMONIA

$^{\dagger}$Work supported by the U. S. Air Force, Office of Scientific Rescarch, under Contrant No. AF 18(600)-1557.Author Institution: Laboratory of Astrophysics and Physical Meteorology., The Johrs Hopkins University“We have observed under high resolution the spectra of $NH_{3}$ and $ND_{3}$ between 1800 $7100 cm^{-1}$ and have analyzed 14 bands of the former and 9 bands of the latter species in that interval. The strongest combinations and overtones of the E vibrations are in general the perpendicular bands. Effective values of the rotation-vibration interaction constants and of $\zeta_{3}$ and $\zeta_{4}$ can be obtained from each analyzed band; these however show small variations in different combinations, so that it is difficult to obtain their limiting value at infinitesimal amplitude with a precision comparable to that of the measurements. One of the interactions responsible for this situation is the Fermi resonance between $2v^{0}_{4}$ and $v_{1}$, which is particularly marked in $ND_{a}$; another is the presence of the low potential barrier to inversion. Table I gives the best available values for the rotational constants in the ground state, their variation with vibration, and the resulting equilibrium dimensions.” [FIGURE