Pyrolysis of Cyclopentadienone: Mechanistic Insights from a Direct Measurement of Product Branching Ratios

Thomas K. Ormond, Adam M. Scheer, Mark R. Nimlos, David J. Robichaud, Tyler P. Troy, Musahid Ahmed, John W. Daily, Thanh Lam Nguyen, John F. Stanton, G. Barney Ellison

Research output: Contribution to journalArticlepeer-review

24 Scopus Citations


The thermal decomposition of cyclopentadienone (C5H4=O) has been studied in a flash pyrolysis continuous flow microreactor. Passing dilute samples of o-phenylene sulfite (C6H4O2SO) in He through the microreactor at elevated temperatures yields a relatively clean source of C5H4=O. The pyrolysis of C5H4=O was investigated over the temperature range 1000-2000 K. Below 1600 K, we have identified two decomposition channels: (1) C5H4=O (+ M) → CO + HC≡C-CH=CH2 and (2) C5H4=O (+ M) → CO + HC≡CH + HC≡CH. There is no evidence of radical or H atom chain reactions. To establish the thermochemistry for the pyrolysis of cyclopentadienone, ab initio electronic structure calculations (AE-CCSD(T)/aug-cc-pCVQZ//AE-CCSD(T)/cc-pVQZ and anharmonic FC-CCSD(T)/ANO1 ZPEs) were used to find ΔfH0(C5H4=O) to be 16 ± 1 kcal mol-1 and ΔfH0(CH2=CH-C≡CH) to be 71 ± 1 kcal mol-1. The calculations predict the reaction enthalpies ΔrxnH0(1) to be 28 ± 1 kcal mol-1rxnH298(1) is 30 ± 1 kcal mol-1) and ΔrxnH0(2) to be 66 ± 1 kcal mol-1rxnH298(2) is 69 ± 1 kcal mol-1). Following pyrolysis of C5H4=O, photoionization mass spectrometry was used to measure the relative concentrations of HCC-CHCH2 and HCCH. Reaction 1 dominates at low pyrolysis temperatures (1000-1400 K). At temperatures above 1400 K, reaction 2 becomes the dominant channel. We have used the product branching ratios over the temperature range 1000-1600 K to extract the ratios of unimolecular rate coefficients for reactions 1 and 2. If Arrhenius expressions are used, the difference of activation energies for reactions 1 and 2, E2 - E1, is found to be 16 ± 1 kcal mol-1 and the ratio of the pre-exponential factors, A2/A1, is 7.0 ± 0.3.

Original languageAmerican English
Pages (from-to)7222-7234
Number of pages13
JournalJournal of Physical Chemistry A
Issue number28
StatePublished - 2015

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

NREL Publication Number

  • NREL/JA-5100-64928


  • continuous flow
  • cyclopentadienone
  • pyrolysis


Dive into the research topics of 'Pyrolysis of Cyclopentadienone: Mechanistic Insights from a Direct Measurement of Product Branching Ratios'. Together they form a unique fingerprint.

Cite this