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

Abstract

The v = 1 → 0 radiative lifetime of NH (X 3 Σ − , v = 1, N = 0) is determined to be τ rad,exp. = 37.0±0.5 stat +2.0 −0.8 sys ms, corresponding to a transition dipole moment of |µ 10 | = 0.0540 +0.0009 −0.0018 D. To achieve the long observation times necessary for direct time-domain measurement, vibrationally excited NH (X 3 Σ − , v = 1, N = 0) radicals are magnetically trapped using helium buffer-gas loading. Simultaneous trapping and lifetime measurement of both the NH(v = 1, N = 0) and NH(v = 0, N = 0) populations allows for accurate extraction of τ rad,exp. . Background helium atoms are present during our measurement of τ rad,exp. , and the rate constant for helium atom induced collisional quenching of NH(v = 1, N = 0) was determined to be k v=1 < 3.9 × 10 −15 cm 3 s −1 . This bound on k v=1 yields the quoted systematic uncertainty on τ rad,exp. . Using an ab initio dipole moment function and an RKR potential, we also determine a theoretical value of 36.99 ms, in agreement with our experimental value. Our results provide an independent determination of τ rad ,10 , test molecular theory, and furthermore demonstrate the efficacy of buffer-gas loading and trapping in determining metastable radiative and collisional lifetimes.

Cold and ultracold NH–NH collisions: The field-free case

“…Cold (T < 1 K) and ultracold (T < 1 mK) molecules offer a wide variety of applications in condensedmatter physics, 1 high-precision spectroscopy, 2-4 physical chemistry, [5][6][7][8][9] and quantum computing. 10,11 In the last few years, techniques have been developed that either form (ultra-) cold molecules by pairing up precooled atoms, e.g., by photoassociation 12 or Feshbach association, 13 or by cooling the molecules directly.…”

“…NH in its electronic X 3 − ground state has been cooled from room temperature using a helium buffer gas and trapped in a magnetic field. 8,[16][17][18] Stark deceleration and electrostatic trapping experiments have been performed on metastable NH(a 1 ), which, in contrast to the X 3 − ground state, exhibits a linear Stark effect. The decelerated NH(a 1 ) molecules can be converted to the ground state by excitation of the A 3 ← a 1 transition followed by spontaneous emission.…”

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

“…Vibrational relaxation is less efficient, since the cross sections for vibrational quenching are typically several order of magnitude smaller than those for translational or rotational relaxation [4]. Several experiments [9,56,72] have seen the vibrational degree of freedom not in thermal equilibrium with the rotational or translational degrees of freedom. Further discussion of internal relaxation of molecules may be found elsewhere [1,4,61].…”

Cold and ultracold NH-NH collisions in magnetic fields

“…Ground-state NH(X 3 − ) has been successfully cooled with a helium buffer gas and confined in a magnetic trap [10,[16][17][18]. Metastable NH(a 1 ) has been Stark decelerated and trapped in an electrostatic field [19].…”