Structural isomers, molecules having the same chemical formula but with atoms bonded in different order, are hard to identify using conventional spectroscopy and mass spectrometry. They exhibit virtually indistinguishable mass spectra when ionized by electrons. Laser mass spectrometry based on photoionization of the isomers has emerged as a promising alternative but requires shaped ultrafast laser pulses. Here we use transform limited femtosecond pulses to distinguish the isomers using two methods. First, we probe doubly charged parent ions with circularly polarized light. We show that the yield of doubly charged ortho-xylene decreases while para-xylene increases over a range of laser intensities when the laser polarization is changed from linear to circular. Second, we probe high harmonic generation from randomly oriented isomer molecules subjected to an intense laser field. We show that the yield of high-order harmonics varies with the positioning of the methyl group in xylene isomers (ortho-, para- and meta-) and is due to differences in the strength of tunnel ionization and the overlap between the angular peaks of ionization and photo-recombination.
A. Alharbi and A. E. Boguslavskiy and D. Austin and N. Thire and D. Wood and P. Hawkins and F. McGrath and A. S. Johnson and I. Lopez-Quintas and B. Schmidt and F. Legare and J. P. Marangos and A. Le and R. Bhardwaj, "Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers," Scientific Reports, vol. 8, no. 1, Nature Publishing Group, Feb 2018.
The definitive version is available at https://doi.org/10.1038/s41598-018-22055-9
International Standard Serial Number (ISSN)
Article - Journal
© 2018 Nature Publishing Group, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution 4.0 License.
01 Feb 2018