Photodissociation transition states characterized by chirped pulse millimeter wave spectroscopy

Kirill Prozument, Joshua H. Baraban, P. Bryan Changala, G. Barratt Park, Rachel G. Shaver, John S. Muenter, Stephen J. Klippenstein, Vladimir Y. Chernyak, Robert W. Field

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


The 193-nm photolysis of CH2CHCN illustrates the capability of chirped-pulse Fourier transform millimeter-wave spectroscopy to characterize transition states. We investigate the HCN, HNC photofragments in highly excited vibrational states using both frequency and intensity information. Measured relative intensities of J = 1–0 rotational transition lines yield vibrational-level population distributions (VPD). These VPDs encode the properties of the parent molecule transition state at which the fragment molecule was born. A Poisson distribution formalism, based on the generalized Franck–Condon principle, is proposed as a framework for extracting information about the transition-state structure from the observed VPD. We employ the isotopologue CH2CDCN to disentangle the unimolecular 3-center DCN elimination mechanism from other pathways to HCN. Our experimental results reveal a previously unknown transition state that we tentatively associate with the HCN eliminated via a secondary, bimolecular reaction.

Original languageEnglish
Pages (from-to)146-151
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number1
StatePublished - 7 Jan 2020


  • Chirped-pulse millimeter-wave spectroscopy
  • Photolysis
  • Transition state
  • Vibrational population distribution
  • Vibrational satellites

ASJC Scopus subject areas

  • General


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