skip to main content

Title: 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

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 selectivelymore » populated in a jet, giving access to K′ = 3 states in IR-UV double resonance.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
  2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China)
  3. (Canada)
Publication Date:
OSTI Identifier:
22493579
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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