Assessment and adjustment approach expands molecular rotors studied with optical centrifuges
Assessment and adjustment approach expands molecular rotors studied with optical centrifuges lead image
The optical centrifuge offers both the directionality of molecular rotation and enables one to spin the molecules to a desired angular frequency. It has garnered use for studying molecular dynamics and properties at extreme levels of rotational excitation. However, elucidating the properties of ultrafast rotating molecules, called molecular superrotors, beyond simple diatomic and triatomic species remains challenging. New work outlines an experimental setup capable of conducting such studies.
MacPhail-Bartley et al. report a strategy for assessing and adjusting centrifuge properties to those of molecular rotors with less-than-favorable “spinnability.” Using optical intensity, angular acceleration and molecular properties as input parameters to their simulations, the group found that slowing centrifuge rotations proved advantageous for spinning molecules with lower polarizability anisotropy-to-moment of inertia ratios. The group then demonstrated examples of how these observations could be used experimentally.
The work paves a way forward for optically centrifuging chiral molecules, whose larger size and moments of inertia make them less amenable to laser spinning.
“Characterizing the centrifuge is extremely important as quite a few side effects of applying strong laser pulses in a gas of molecules may be mistaken for the effects of rotational excitation,” said author Valery Milner.
The group’s experimental centrifuges employed one of three characterizations: a gas-independent “pileup” method, cross-correlation frequency-resolved optical grating techniques and a coherent Raman scattering approach that provides direct evidence of the working centrifuge.
“Our ‘slow centrifuge’ should allow rotational control of many more molecular species than those that have been studied so far,” Milner said.
He hopes expanding the control of optical centrifuges will stimulate new theoretical proposals for its use. He said the group next looks to apply the slow centrifuge to more complex molecular systems.
Source: “Laser control of molecular rotation: Expanding the utility of an optical centrifuge,” by Ian MacPhail-Bartley, Walter W. Wasserman, Alexander Milner, and Valery Milner, Review of Scientific Instruments (2020). The article can be accessed at https://doi.org/10.1063/1.5140358 .
