Zeeman spectroscopy of CaH molecules in a magnetic trap

Abstract

In a recent experiment ͓Weinstein et al., Nature 395, 148 ͑1998͔͒ we magnetically trapped 10 8 ground-state calcium monohydride molecules, CaH(X 2 ⌺,vЉϭ0, JЉϭ0). The molecules were prepared by laser ablation of a solid sample of CaH 2 and loaded via thermalization with a cold (Ͻ1 K͒ 3 He buffer gas. The magnetic trap was formed by superconducting coils arranged in the anti-Helmholtz configuration. The detection was done by laser fluorescence spectroscopy excited at 635 nm ͑in the B 2 ⌺,vЈϭ0ϪX 2 ⌺,vЉϭ0 band͒ and detected at 692 nm ͑within the B,vЈϭ0 ϪX,vЉϭ1 band͒. Both a photomultiplier tube and a CCD camera were used. Due to the thermalization of molecular rotation, only a transition from the lowest rotational state could be detected at zero field, NЈϭ1, JЈϭ3/2←NЉϭ0, JЉϭ1/2. In the magnetic field this rotational transition splits into two features, one shifted towards lower and one towards higher frequencies. The measured shifts are linear in field strength and indicate a small difference ͑0.02 B ) in the magnetic moments between the ground and excited states. Here we present a theoretical analysis of the observed magnetic shifts. These are identified as arising from a rotational perturbation of the B 2 ⌺,vЈϭ0 state by a close-lying A 2 ⌸,vЈϭ1 state that lends the B state some of its A character. We find that the Hamiltonian can be well approximated by a 3ϫ3 matrix built out of elements that connect states from within the ⌺-doublet and the 2 ⌸ 3/2 manifolds. The interaction parameter describing the ⌺Ϫ⌸ coupling in the Zeeman Hamiltonian is determined from the observed shifts and the field-free molecular parameters of CaH given by Berg and Klyning ͓Phys. Scr. 10, 331 ͑1974͔͒ and by Martin ͓J. Mol. Spectrosc 108, 66 ͑1984͔͒.

High-Flux Beam Source for Cold, Slow Atoms or Molecules

“…However, for nearly every species we have tried (here and in many related experiments), it has been possible to achieve large values of N by a suitable choice of precursor material. For example, under operating conditions similar to those used here, we have obtained N 10 12 -10 14 for a variety of metal atoms and N 10 11 -10 13 for many species of diatomic molecules (including radicals) [25][26][27][28]. In addition -subject to limitations of cooling power or gas load-the source could be run at lower temperatures, higher repetition rates, or with higher extraction efficiency (e.g., by using several separated exit holes).…”

Collisions of paramagnetic molecules in magnetic fields: An analytic model based on Fraunhofer diffraction of matter waves

“…The CaH molecule, employed previously in thermalization experiments with a He buffer gas [15], [16], has a rotational constant B = 4.2766 cm −1 and a spin-rotational interaction parameter γ = 0.0430 cm −1 [27]. Such values of molecular constants result in an essentially perfect mixing (and alignment) of the molecular states for field strengths H ≥ 0.1 Tesla, see Sec.…”

“…The "hard shell" of the potential energy surface at this collision energy is shown in Fig. 3, and the Furthermore, since the nuclear spin of 16 O is zero and the electronic ground state antisymmetric (a 3 Σ − g state), only rotational states with an odd rotational quantum number N are allowed. We will assume that the O 2 molecule is initially in its rotational ground state, |N = 1, J = 0, M = 0 .…”

“…As a result, the Zeeman eigenfunctions of a 2 Σ molecule are given by a linear combination of the field-free wavefunctions (16),…”

Time-Resolved Laser Spectroscopy

“…[47][48][49][50][51] Excited state diatomic radicals are often produced in chemical reactions, both in the laboratory and in the atmosphere. [52][53][54] The spectrum of CaH, for example, is frequently found -11 -in cool stars [55] and in sun spots. [52] In order to describe these kinds of chemical reactions in detail it is of great importance to know the characteristics of the molecular electronic transitions involved which is also essential in astrophysics.…”