The ν3 vibrational spectrum of the free ammonium ion (NH4+)

Abstract

The ν₃ band of the ammonium ion was measured near 3.0 μm with a color center laser spectrometer using the technique of velocity modulated absorption spectroscopy. NH₄⁺ was produced in an ac discharge containing 0.1 Torr of nH₃ and 1.5 Torr of H₂. Seventy individual transitions were measured with an accuracy of 1×10⁻⁶ and assigned to q⁰, P⁺, and R⁻ branches of a tetrahedral molecule. The constants derived in a preliminary analysis are: ν^eff₀=3342.540 2(97) cm⁻¹, B₀+B₁−2B₁χ₃=11.110 8(35) cm⁻¹, B₁−B₀=−0.050 71(45) cm⁻2u1, and D=8.5(2.6)×10⁻⁵ cm⁻¹. (AIP)