Determination of the Einstein A coefficient for the ?→? transition of ammonia-d3

Abstract

The fluorescence of ND₃ has been observed for excitation into the ?←? system at 213.86 nm. The quantum yield for this transition is 8.3×10⁻⁵. With this quantum yield and the known rotational linewidth of the upper electronic state, an Einstein A coefficient is obtained that compares favorably with a value calculated from the emission intensity and absorption strength of the (ν₁′,ν₂′=0,0) ↔ (ν₁^″,ν₂^″ =0,2) vibronic bands. The average of these two values is A=3.6±0.3×10⁷ sec⁻¹. The underlying continuum of the ?←? absorption system, attributed to the predissociation of ND₃, is invoked to explain most of the discrepancy between the above value for A and that predicted by the equation of Strickler and Berg. A weaker, more diffuse emission has also been observed from ND₃ for excitation into the ?←? system at 206.24 nm with fluorescence quantum yield of 1.₁×10⁻⁵.