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Title: Photodissociation of dicarbon: How nature breaks an unusual multiple bond

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
ORCiD logo [1];  [1]; ORCiD logo [2]; ORCiD logo [1];  [1]; ORCiD logo [3];  [4]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of New South Wales, Sydney, NSW (Australia)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Univ. of Florida, Gainesville, FL (United States)
+ Show Author Affiliations

The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ∙mol-1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ∙mol-1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Univ. of New South Wales, Sydney, NSW (Australia)
Sponsoring Organization:
Australian Research Council; Center of Excellence in Exciton Science; USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1860679
Report Number(s):
LLNL-JRNL-824856; 1038447
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 52 Vol. 118; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
comets
dicarbon
photodissociation