Probing cis-trans isomerization in the S1 state of C2H2 via H-atom action and hot band-pumped IR-UV double resonance spectroscopies
Author(s)Changala, P. Bryan; Baraban, Joshua H.; Merer, Anthony J.; Field, Robert W.; Baraban, Joshua Herschel; Field, Robert W; ... Show more Show less
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We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C[subscript 2]H[subscript 2], in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm[superscript −1] below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C[subscript 2]H + H sets in roughly 1100 cm[superscript −1] below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K' − ℓ" = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ" > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ" = 2 states can be selectively populated in a jet, giving access to K' = 3 states in IR-UV double resonance.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
Journal of Chemical Physics
American Institute of Physics (AIP)
Changala, P. Bryan, Joshua H. Baraban, Anthony J. Merer, and Robert W. Field. “Probing Cis-Trans Isomerization in the S1 State of C2H2 via H-Atom Action and Hot Band-Pumped IR-UV Double Resonance Spectroscopies.” J. Chem. Phys. 143, no. 8 (August 28, 2015): 084310. © 2015 AIP Publishing LLC.
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