Abstract
The structure and dynamics of high-n Rydberg states belonging to series converging to the (v(+) = 0, N(+) = 0-2) levels of the X(+) (2)Σ(g)(+)electronic ground state of HD(+) were studied by high-resolution spectroscopy from the GK (1)Σ(g)(+) (v = 1, N = 1) state under field-free conditions. Three effects of g/u-symmetry breaking were detected: (i) Single-photon transitions from the GK (v = 1, N = 1) state of gerade symmetry to the 30d21 and 31g22 Rydberg states of gerade symmetry were observed after careful compensation of the stray electric fields. (ii) The singlet 61p12 Rydberg state of ungerade symmetry was found to autoionize to the N(+) = 0, ℓ = 2 ionization continuum of gerade symmetry with a lifetime of 77(10) ns. (iii) Shifts of up to 20 MHz induced by g/u-symmetry mixing were measured for members of the np11 Rydberg series which lie close to nd21 Rydberg states. These observations were analyzed in the framework of multichannel quantum-defect theory. From the observed level shifts, the off-diagonal eigenquantum-defect element μ(pd) of singlet-π symmetry was determined to be 0.0023(3) and the corresponding autoionization dynamics could be characterized. The ionization energy of the GK (v = 1, N = 1) state of HD was determined to be 12 710.544 23(10) cm(-1).
Highlights
In the last decade, several methods have become available to prepare molecules in the gas phase at low temperatures [1,2,3,4]
In the case of paramagnetic atoms and molecules which can be entrained in a supersonic beam, multistage Zeeman deceleration [16] and related techniques [17, 18] are the methods of choice: The phase-space density of atoms and molecules in supersonic beams is high and is preserved by phase-stable operation of the decelerator [19, 20], the method can be quantumstate selective [21], the final velocity of the particles can be controlled and tuned over a wide range [22,23,24], and the decelerated particles can be loaded into a magnetic trap [25, 26] for observation of slow decay processes or spectroscopic measurements requiring long observation times
We describe here the use of multistage Zeeman deceleration to generate slow and velocity-tunable beams of He2 molecules in the metastable a 3Σ+u state in a setup tailored for future applications in precision spectroscopy
Summary
Several methods have become available to prepare molecules in the gas phase at low temperatures [1,2,3,4]. Cold molecules with translational temperatures in the range 100 mK–1 K may find applications in precision spectroscopy [5, 6] and in the study of chemical reactivity at very low collision energies and very high energy resolution [7, 8]. They may represent the starting point for further cooling steps toward the ultracold regime below 1 mK [9,10,11,12,13].
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