Perpendicular Vibrations of the Ammonia Molecule

The vibration frequency ν₂ of NH₃ is identified by means of the combination bands ν₂±ν₃ at 2.2{μ} and 4.0{μ}, in each of which the spacing between component bands is about 16 cm^-1. From the difference band the numerical value of ν₂ is fixed at 3415 cm^-1. The fundamental band may be recognized in the weak and complex background of the absorption at 3{μ}. The coefficient ζ₂ of the vibrational angular momentum is approximately +0.6.The second perpendicular fundamental band at 6{μ} is partially resolved, and is in good agreement with the expected pattern if ζ₄ equals -0.3. The indicated value of ν₄ is 1628 cm^-1. The numerical values of ζ₂ and ζ₄ do not agree well with those predicted theoretically.The parallel component of 2ν₄ is found at 3220 cm^-1, and two pairs of parallel combination bands, ν₁+ν₃ at 4270 and 4303 cm^-1 and 2ν₄+ν₃ at 4177 and 4217 cm^-1.