The cold boroncarbide free radical (BC X  4Σ) has been produced in a pulsed discharge free jet expansion using a precursor mixture of trimethylborane in high pressure argon. High resolution laser induced fluorescencespectra have been obtained for the B  4ΣX4Σ and E  4Π–X4Σ band systems of both 11BC and 10BC. An optical-optical double resonance (OODR) scheme was implemented to study the finer details of both band systems. This involved pumping a single rotational level of the B state with one laser and then recording the various allowed transitions from the intermediate B state to the final E state with a second laser by monitoring the subsequent EX ultraviolet fluorescence. In this fashion, we were able to prove unambiguously that, contrary to previous studies, the spin-spin constant λ is negative in the ground state and positive in the B4Σexcited state. It has been shown that λ″ < 0 is in fact expected based on a semiempirical second order perturbation theory calculation of the magnitude of the spin-spin constant. The OODR spectra have also been used to validate our assignments of the complex and badly overlapped E 4Π–X4Σ 0-0 and 1-0 bands of 11BC. The EX 0-0 band of 10BC was found to be severely perturbed. The ground state main electron configuration is …3σ22120 and the derived bond lengths show that there is a 0.03 Å contraction in the B state, due to the promotion of an electron from the 4σ antibonding orbital to the 5σ bonding orbital. In contrast, the bond length elongates by 0.15 Å in the E state, a result of promoting an electron from the 5σ bonding orbital to the 2π antibonding orbitals.

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Published in The Journal of Chemical Physics, v. 143, no. 2, article 224308, p. 1-11.

© 2015 AIP Publishing LLC.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in The Journal of Chemical Physics, v. 143, no. 2, article 224308, p. 1-11 and may be found at http://dx.doi.org/10.1063/1.4936255.

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This material is based upon work supported by the National Science Foundation under Grant No. CHE-1106338.

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