Nuclear spin relaxation in cold atom-molecule collisions

Abstract

We explore the quantum dynamics of nuclear spin relaxation in cold collisions of ${}^1{\Sigma }^{+}$ molecules with structureless atoms in an external magnetic field. To this end, we develop a rigorous coupled-channel methodology, which accounts for rotational and nuclear spin degrees of freedom of ${}^1{\Sigma }^{+}$ molecules, their interaction with an external magnetic field, as well as for anisotropic atom-molecule interactions. We apply the methodology to study collisional relaxation of the nuclear spin sublevels of ${}^{13}$CO molecules immersed in a cold buffer gas of ${}^4$He atoms. We find that nuclear spin relaxation in the ground rotational manifold of CO occurs extremely slowly due to the absence of direct couplings between the nuclear spin sublevels. The rates of collisional transitions between the $N=1$ nuclear spin states of CO are generally much higher due to the direct nuclear spin-rotation coupling between the states. These transitions obey selection rules, which depend on the values of space-fixed projections of rotational and nuclear spin angular momenta for the initial and final molecular states. For some initial states, we also observe a strong magnetic field dependence, which can be understood using the first Born approximation. We use our calculated nuclear spin relaxation rates to investigate the thermalization of a single nuclear spin state of CO$(N=0)$ immersed in a cold buffer gas of He. The calculated nuclear spin relaxation times ($T_1\simeq 0.5$ s at $T=1$ K) display a steep temperature dependence decreasing rapidly at elevated temperatures due to the increased population of rotationally excited states, which undergo nuclear spin relaxation at a much faster rate. Thus, long relaxation times of $N=0$ nuclear spin states in cold collisions with buffer gas atoms can only be maintained at sufficiently low temperatures ($kT\ll 2B_e$), where $B_e$ is the rotational constant.

41 pages, 12 figures

References in corpus (15)

• Cold molecules: Progress in Quantum Engineering of Chemistry and Quantum Matter
• Feshbach resonances in ultracold atomic and molecular collisions: threshold behaviour and suppression of poles in scattering lengths
• Ultracold Rb-OH collisions and prospects for sympathetic cooling
• Cold N+NH Collisions in a Magnetic Trap
• Collisions Between Ultracold Molecules and Atoms in a Magnetic Trap
• Mechanism of Collisional Spin Relaxation in Triplet-Sigma Molecules
• Optical cycling of AlF molecules
• High Sensitivity Microwave Spectroscopy in a Cryogenic Buffer Gas Cell
• Efficient method for quantum calculations of molecule - molecule scattering properties in a magnetic field
• Spectroscopy on the $A^1\Pi \leftarrow X^1{\Sigma }^{+}$ Transition of Buffer-Gas Cooled AlCl
• Quantum spin state selectivity and magnetic tuning of ultracold chemical reactions of triplet alkali-metal dimers with alkali-metal atoms
• Saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride molecules
• Collision-induced C_60 rovibrational relaxation probed by state-resolved nonlinear spectroscopy
• Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + CH2(X) collisions
• Total angular momentum representation for state-to-state quantum scattering of cold molecules in a magnetic field

Cited by in corpus (4)

• Low temperature decoherence dynamics in molecular spin systems using the Lindblad master equation
• Ultracold molecular collisions in magnetic fields: Efficient incorporation of hyperfine structure in the total rotational angular momentum representation
• Hyperfine and Zeeman interactions in ultracold collisions of molecular hydrogen with atomic lithium
• Highly spin-polarized molecules via collisional microwave pumping