Evidence of rotational autoionization in the threshold region of the photoionization spectrum of CH{sub 3}

Journal Article · Mon Dec 01 04:00:00 EST 1997 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.475282· OSTI ID:550461

Litorja, M; Ruscic, B ^[1]

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1. Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439-4831 (United States)

The photoionization spectrum of the threshold region of CH{sub 3} equilibrated at room temperature has been recorded and compared to the zero electron kinetic energy (ZEKE) spectrum of Blush {ital et al.} [J. Chem. Phys. {bold 98}, 3557 (1993)]. The ionization onset region is at {approximately}70cm{sup {minus}1} higher energy than previous high-temperature photoionization work [Chupka and Lifshitz, J. Chem. Phys. {bold 48}, 1109 (1967)], but still {approximately}34cm{sup {minus}1} lower than that implied by invoking only direct ionization. The residual discrepancy can be accounted for by including fully allowed quadrupole-induced and partially allowed dipole-induced rotational autoionization, thus making the observed onset completely congruous with the ZEKE ionization potential. In addition, the fragment appearance potential of CH{sub 3}{sup +} from CH{sub 4} was redetermined by accurate fitting as AP{sub 0}(CH{sub 3}{sup +}/CH{sub 4})=14.322{plus_minus}0.003eV. With the very precise ZEKE ionization potential, this yields the best current value for the bond dissociation energy in methane, D{sub 0}(H{endash}CH{sub 3})=4.484{plus_minus}0.003eV=103.40{plus_minus}0.07kcal/mol (104.96{plus_minus}0.07kcal/mol at 298 K). {copyright} {ital 1997 American Institute of Physics.}

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 550461
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 23 Vol. 107; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
AUTOIONIZATION
DISSOCIATION ENERGY
IONIZATION POTENTIAL
METHANE
METHYL RADICALS
PHOTOIONIZATION
ROTATIONAL STATES