The role of the intermediate state in angle-resolved photoelectron studies using (2 + 1) resonance-enhanced multiphoton ionization of the chiral terpenes, α-pinene and 3-carene

Abstract

Photoelectron angular distributions (PADs), ranging up to the maximum 6th order Legendre polynomial term set by the Yang theorem, have been recorded for the (2 + 1) resonance enhanced multiphoton ionization (REMPI) of two terpene isomers, 3-carene and α-pinene, employing femtosecond lasers and electron velocity map imaging detection. PAD measurements made with coincident photoion detection allow ion fragmentation effects to be assessed. Using circular polarization and enantiomerically pure samples the PAD measurements are extended to include chiral (odd) Legendre polynomial terms, and these are analysed and discussed as multiphoton photoelectron circular dichroism (MP-PECD). Comparisons are also made with single photon (synchrotron radiation) PECD of these compounds. Although for a given compound a common final cation state is reached, pronounced differences are observed between PECD and MP-PECD, and between the alternative identified REMPI intermediate states in the case of MP-PECD.

GRAPHICAL ABSTRACT

KEYWORDS:

• Circular dichroism
• photoelectron specroscopy
• angular distribution
• photoionization
• terpenes

Acknowledgements

We thank Kevin Schug for providing the 3-carene absorption spectrum data from ref [32].

The authors gratefully thank Maurice Janssen for his enthusiastic support and suggestions to use the electron-ion imaging apparatus at Nijmegen, and Wybren-Jan Buma for helping facilitate this.

Daniel Horke and Anders Huits are thanked for their help with data acquisition in Nijmegen and Yu Zhang and Adam Wyatt for their assistance at Artemis.

Finally, we thank Dave Parker for welcoming our team to the Institute for Molecules and Materials at Radboud University and ensuring a productive and stimulating visit.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was undertaken as part of the ASPIRE Innovative Training Network, which has received funding from the European Union’s Horizon 2020 research and innovation framework programme under the Marie Sklodowska-Curie Action, Grant No. 674960. HG and DPS thank ASPIRE for ESR Fellowships.

Funding for Laser facility access was received from EU H2020 research and innovation framework programme (grant agreement 654148, LASERLAB-EUROPE ) award #LLAMS002376 (IP) for work in Nijmegen, and from the STFC (UKRI) for access to the Central Laser Facility “Artemis” system, award #17220004 (IP and KLR).

RSM thanks the Royal Society for a University Research Fellowship (UF100047, UF150655).