Probing cis-trans isomerization in the S{sub 1} state of C{sub 2}H{sub 2} via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

Journal Article · Fri Aug 28 00:00:00 EDT 2015 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4929588· OSTI ID:22493579

Changala, P. Bryan; Baraban, Joshua H.; Merer, Anthony J. ^[1]

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1. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China)

We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S{sub 1} state of acetylene, C{sub 2}H{sub 2}, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm{sup −1} below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C{sub 2}H + H sets in roughly 1100 cm{sup −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{sup ′′} = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ{sup ′′} > 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{sup ′′} = 2 states can be selectively populated in a jet, giving access to K′ = 3 states in IR-UV double resonance.

• OSTI ID: 22493579
• Journal Information: Journal of Chemical Physics, Vol. 143, Issue 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION SPECTROSCOPY
ACETYLENE
ATOMS
DIFFUSION BARRIERS
FLUORESCENCE SPECTROSCOPY
GROUND STATES
ISOMERIZATION
LASER RADIATION
MULTI-PHOTON PROCESSES
PHOTOIONIZATION
PREDISSOCIATION
QUENCHING
RESONANCE
ROTATIONAL STATES
S STATES
SELECTION RULES
TUNNEL EFFECT
VIBRATIONAL STATES