Electronic spectrum of dicyanoacetylene. 2. Interpretation of the 2800 Å transition

Gad Fischer*, G. Dana Johnson, D. A. Ramsay, I. G. Ross

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)

    Abstract

    The 2800 Å forbidden 1Σu-1Σg+ transition of dicyanoacetylene shows conventional vibronic origins due to the two πg vibrations and a third involving the lower πu vibration. For the latter we argue against a magnetic dipole mechanism and propose that the intensity is electric dipole, involving coupling to a π* ← n state of reduced point symmetry (C∞v or less). The strongest band in the spectrum may be another such origin, but there is a competing assignment and neither meets expectations of intensities in related bands. While the vibrational structure is emphatic that the excited-state remains linear, the rotational constants extracted from the principal bands, all double-headed and violet-degraded (ΔB0 positive), present problems. The apparent contraction or bending of the molecule thus indicated can be countered by large corrections that yield negative values of the equilibrium constant ΔBe. The size of these corrections and further B values extracted from sequence bands indicate that rotational constants are not uniformly linear in the quantum numbers of the bending vibrations.

    Original languageEnglish
    Pages (from-to)10637-10641
    Number of pages5
    JournalJournal of Physical Chemistry A
    Volume107
    Issue number49
    DOIs
    Publication statusPublished - 11 Dec 2003

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