Multiphoton ionization studies of IR multiphoton dissociation: direct C-H bond cleavage in methanol

Journal Article · Thu Jun 05 04:00:00 EDT 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100403a016· OSTI ID:5697079

Bomse, D S; Dougal, S; Woodin, R L

The multiphoton ionization (MPI) spectra of products generated by infrared multiphoton dissociation (IRMPD) of CH/sub 3/OH and CD/sub 3/OH are reported. Over the 445-510-nm dye laser range covered, the MPI spectral features are predominantly due to hydroxymethyl radicals, CH/sub 2/OH and CD/sub 2/OH, with a very minor contribution from CH/sub 3/. At short reaction times no formaldehyde is detected. The lowest energy methanol decomposition pathway, to CH/sub 3/ + OH, is not explored because resonantly enhanced CH/sub 3/, MPI is inefficient within the wavelength range available. Selective IRMPD of CD/sub 3/OH in 1 Torr of a 1:1 CH/sub 3/OH:CD/sub 3/OH mixture yields exclusively CD/sub 2/OH at short (200 ns) reaction times demonstrating direct C-H bond cleavage does occur in competition with the lower enthalpy reaction (C-O bond breaking). The upper bound for the branching ratio to CH/sub 2/OH + H (relative to CH/sub 3/ + OH) is 20% based on comparison with shock tube experiments. The time scale for CH/sub 2/OH produced bimolecularly is consistent with the rate constant for H-atom abstraction by OH from methanol. The excitation proceeds via a resonant two-photon absorption to a 3p Rydberg level (screening constant delta = 0.65) followed by one more photon to exceed the ionization threshold. Failure to observe two-photon fluorescence is consistent with this assignment of the initial step as a p-to-p type excitation.

• Research Organization: Exxon Research and Engineering Co., Annandale, NJ
• OSTI ID: 5697079
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:12; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
ALCOHOLS
BINDING ENERGY
CARBON DIOXIDE LASERS
CHEMISTRY
DATA
DISSOCIATION
DYE LASERS
ENERGY
ENTHALPY
EXPERIMENTAL DATA
FOURIER TRANSFORM SPECTROMETERS
GAS LASERS
HYDROXY COMPOUNDS
INFORMATION
LASERS
LIQUID LASERS
MEASURING INSTRUMENTS
METHANOL
MULTI-PHOTON PROCESSES
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMISTRY
PHYSICAL PROPERTIES
SPECTROMETERS
SPECTROSCOPY
THERMODYNAMIC PROPERTIES