Browsing by Author "Lee, T. J."

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    High-accuracy quartic force field calculations for the spectroscopic constants and vibrational frequencies of 1¹A′ 𝑙-C₃H⁻: A possible link to lines observed in the horsehead nebula photodissociation region
    Fortenberry, Ryan Clifton; Huang, X. C.; Crawford, T. Daniel; Lee, T. J. (IOP Publishing Ltd., 2013-07)
    It has been shown that rotational lines observed in the Horsehead nebula photodissociation region (PDR) are probably not caused by l-C3H+, as was originally suggested. In the search for viable alternative candidate carriers, quartic force fields are employed here to provide highly accurate rotational constants, as well as fundamental vibrational frequencies, for another candidate carrier: 1(1)A'C3H-. The ab initio computed spectroscopic constants provided in this work are, compared to those necessary to define the observed lines, as accurate as the computed spectroscopic constants for many of the known interstellar anions. Additionally, the computed D-eff for C3H is three times closer to the D deduced from the observed Horsehead nebula lines relative to l-C3H+. As a result, 1(1)A'C3H- is a more viable candidate for these observed rotational transitions. It has been previously proposed that at least C6H- may be present in the Horsehead nebular PDR formed by way of radiative attachment through its dipole-bound excited state. C3H- could form in a similar way through its dipole-bound state, but its valence excited state increases the number of relaxation pathways possible to reach the ground electronic state. In turn, the rate of formation for C3H- could be greater than the rate of its destruction. C3H- would be the seventh confirmed interstellar anion detected within the past decade and the first CnH- molecular anion with an odd n.
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    The possible interstellar anion CH₂CN⁻: spectroscopic constants, vibrational frequencies, and other considerations
    Fortenberry, Ryan Clifton; Crawford, T. Daniel; Lee, T. J. (IOP Publishing Ltd., 2013-01)
    The A B-1(1) <- (X) over tilde (1)A' excitation into the dipole-bound state of the cyanomethyl anion (CH2CN-) has been hypothesized as the carrier for one diffuse interstellar band. However, this particular molecular system has not been detected in the interstellar medium even though the related cyanomethyl radical and the isoelectronic ketenimine molecule have been found. In this study, we are employing the use of proven quartic force fields and second-order vibrational perturbation theory to compute accurate spectroscopic constants and fundamental vibrational frequencies for (X) over tilde (1)A' CH2CN- in order to assist in laboratory studies and astronomical observations.