Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + CH2(X) collisions

Abstract

We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wavefunction. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [CH2(X)] with He atoms. To this end, two highly accurate three-dimensional potential energy surfaces (PESs) of the He-CH2(X) complex are developed using the state-of-the-art CCSD(T) method and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH2, CHD, and CD2 molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 uK -- 1 K) and magnetic fields (0.01 - 1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-CH2(X) molecules in a magnetic trap. Furthermore, we find that ortho-CH2 undergoes collision-induced spin relaxation much more slowly than para-CH2, which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.

References in corpus (21)

• A High Phase-Space-Density Gas of Polar Molecules
• Cold and Ultracold Molecules: Science, Technology, and Applications
• Collisional decoherence observed in matter wave interferometry
• Hund's paradox and the collisional stabilization of chiral molecules
• Magnetic trapping and Zeeman relaxation of imidogen (NH X-triplet-Sigma)
• Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals
• Magnetic field effects in ultracold molecular collisions
• Electrostatic extraction of cold molecules from a cryogenic reservoir
• Cold heteromolecular dipolar collisions
• Cold N+NH Collisions in a Magnetic Trap
• Production of ultracold NH molecules by sympathetic cooling with Mg
• Alternating gradient focusing and deceleration of large molecules
• Low-energy collisions of NH3 and ND3 with ultracold Rb atoms
• Mechanism of Collisional Spin Relaxation in Triplet-Sigma Molecules
• Far-Infrared detection of methylene
• Improved setup for producing slow beams of cold molecules using a rotating nozzle
• Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap
• Cold guided beams of water isotopologs
• Manipulating the motion of large neutral molecules
• Cold collisions of complex polyatomic molecules
• A fundamental limit to the efficiency of spin-exchange optical pumping of 3He nuclei

Cited by in corpus (4)

• Cold collisions of heavy ${}^2\Sigma$ molecules with alkali-metal atoms in a magnetic field: Ab initio analysis and prospects for sympathetic cooling of SrOH${(}^2\Sigma )$ by Li(${}^2$S)
• Spin coherence and optical properties of alkali-metal atoms in solid parahydrogen
• Nuclear spin relaxation in cold atom-molecule collisions
• Elastic and inelastic collisions of ${}^2\Sigma$ molecules in a magnetic field