Centrifuge spectroscopy probes extreme rotational states

A new spectroscopic technique for studying electronically excited molecules at very high angular momentum has been developed and tested by scientists in Canada.

The team, from the University of British Columbia, headed by Valery Milner, have used an optical centrifuge to excite oxygen to rotational states that otherwise can’t be reached. An optical centrifuge combines two laser pulses to create an intense electric field which undergoes angular acceleration to drive molecules into the remarkable angular momentum states. The super rotation state reached for oxygen in the study is equivalent to heating the molecule to 50,000K, a temperature that is too hot for the molecule to survive. A spectroscopic technique called resonance-enhanced multi-photon ionisation was combined with the centrifuge and by carefully controlling and calibrating the rotational speed of the centrifuge a spectrum can be viewed as a two-dimensional function of photon energy and angular momentum.

‘It greatly simplifies the spectra,’ says Aleksey Korobenko, the lead scientist on this study. ‘Even when the photon energy branches are overlapping, you can track one by one the rotational peaks which you can’t otherwise separate out.’

The spectrum is a function of both photon energy (horizontal direction) and angular momentum (vertical direction)

The technique is not limited to observations of the rotational structure of electronic transitions in molecules, as demonstrated in the current study. Molecules excited to the extreme rotational states realisable by using the optical centrifuge are expected to exhibit many intriguing properties, from THz emission, rotation-induced magnetism and macroscopic gas vortices, to unusual surface scattering behaviours and selective bond breaking.

Ilya Averbukh, an expert in laser control and molecular rotation at the Weizmann Institute of Science in Israel, has high hopes for the technique. ‘The approach opens the door for testing our theoretical proposal on using ultra-fast molecular rotation to control molecular scattering from solid surfaces, an area of both fundamental and applied significance. Centrifuge spectroscopy adds an important component to the arsenal of tools required for this study.’

Milner’s group is now applying the technique to two long-term projects. The first is an investigation into fundamental aspects of molecule–surface scattering, in the realm of super rotation, by observing the quantum state distribution of the molecules before and after collision. In the second project they will be controlling and studying molecular rotation inside highly correlated quantum systems, such as superfluid helium.

Related Content

Images show atom 'spinning top' control

12 December 2010 News Archive

news image

Precession of quantum mechanical angular momentum in atomic oxygen can be directed and pictured, potentially allowing more de...

Detecting chirality

28 July 2014 Premium contentFeature

news image

Katia Moskvitch finds out about the latest techniques to determining a molecule’s chirality

Most Read

UC Davis chemist sentenced to four years over explosion

19 November 2014 News and Analysis

news image

Postdoc sentenced over attempt to make explosive device and reckless disposal of hazardous waste

Spanish fly

10 October 2013 Podcast | Compounds

news image

Helen Scales looks at cantharidin, the active ingredient in this famous aphrodisiac

Most Commented

Beetle behind breath test for bank notes

17 November 2014 Research

news image

Photonic crystal inks inspired by longhorn beetle could help to fight counterfeiting

Nanostripe controversy in new twist

24 November 2014 Research

news image

Creator of striped nanoparticles insists questions over structures have already been answered and accuses critics of a 'perso...