A magnetically focused molecular beam source for deposition of spin-polarised molecular surface layers

Abstract

Separating molecular spin isomers is a challanging task, with potential applications in various fields ranging from astrochemistry to magnetic resonance imaging. A new promissing method for spin-isomer separation is magnetic focusing, a method which was shown to be capable of producing a molecular beam of ortho-water. Here, we present results from a modified magnetic focusing apparatus and show that it can be used to separate the spin isomers of acetylene and methane. From the measured focused profiles of the molecular beams and a numerical simulation analysis we provide estimations for the spin purity and the significantly improved molecular flux obtained with the new setup. Finally, we discuss the spin-relaxation conditions which will be needed to apply this new source for measuring NMR signals of single surface layer.

Quantum State-Resolved Characterization of a Magnetically Focused Beam of ortho-H2O

“…[32][33][34] However, the conversion of ortho-H 2 O to para-H 2 O is not the relevant criteria for assessing potential hyperpolarised NMR applications; the questions are rather how and where do the spins transfer to the solid/adsorbed phase as well as the magnitude of the T 1 time required for thermodynamic spin equilibrium to be reached. 24 Accordingly, ongoing work relying on the methodology described herein is aimed at improving our molecular-level understanding of the processes responsible for the decay in sample magnetisation and erosion of the NSI enrichment in the adsorbed/condensed phase, as well as the underlying relaxation mechanisms and rates. NSI should also facilitate investigations into the dynamics and rates for heterogeneous NSI interconversion, a process which lead to an erosion of the NSI enrichment when molecules interact with surfaces or condense onto a solid.…”

“…The schematics of the apparatus used to prepare water vapour significantly enriched in the ortho-H 2 O nuclear spin isomer is presented in Figure 1 as these latter experience a restoring force that bends their trajectories back onto the beam axis as a result of their interaction with the strong inhomogeneous hexapolar field afforded by the magnetic lens. 23,24 Simulations suggest the flux of these latter reaches a maximum at a location ∼ 1.5 m downstream from the exit of the magnetic lens (i.e., TOF position 2, Figure 2c).…”

Setting benchmarks for modelling gas–surface interactions using coherent control of rotational orientation states

“…Two types of calculations are used to simulate the propagation of the molecular waves through the apparatus. Within the two hexapole fields (Hex1 and Hex2), which are characterised by large magnetic field gradients and correspondingly pure m I , m J states 32 , semi-classical ray tracing calculations are used to determine the particle trajectories and corresponding transmission probabilities for each state 63 . For the majority of the beam line, contained between these two hexapole fields, the propagation of the wave function needs to be calculated coherently.…”

Transfer-matrix theory of surface spin-echo experiments with molecules

“…Thus, we need only determine the values of P R0 for a specific magnetic lens. These can be found via semi-classical calculations [53,87], may be measured experimentally [87] or may potentially be determined by solving the full 3D Schrödinger equation within the lens.…”

“…The relative probabilities used for the state selector probabilities P R0 and the detector coefficients c R D are given in Table I. Where applicable, the parameters above were chosen to match those in the supplementary information of Godsi et al [53], apart for the relative probabilities in Table I. The relative probabilities in Table I were obtained from improved semi-classical calculations of the molecular propagation through the magnetic lens [53,87].…”