Time-Domain Measurement of Spontaneous Vibrational Decay of Magnetically Trapped NH

Abstract

The \(v = 1 \to 0\) radiative lifetime of \(NH (X^3 \Sigma^-, v=1, N=0)\) is determined to be \(\tau_{rad,\text{exp.}} = 37.0 \pm 0.5_{\text{stat}}{}^{+2.0} _{-0.8\text{syst}}\) miliseconds, corresponding to a transition dipole moment of \(|\mu_{10}| = 0.0540_{{-0.0018}^{+0.0009}}\) D. To achieve the long observation times necessary for direct time-domain measurement, vibrationally excited \(NH (X^3 \Sigma^-, v=1)\) radicals are magnetically trapped using helium buffer-gas loading. The rate constant for background helium-induced collisional quenching was determined to be \(k_{v=1}<3.9 \times 10^{-15}cm^3s^{-1}\), which yields the quoted systematic uncertainty on τrad,exp.. With a new ab initio dipole moment function and a Rydberg-Klein-Rees potential, we calculate a lifetime of 36.99 ms, in agreement with our experimental value.