High resolution study of the. nu. sub 1 vibration of CH sub 3 by coherent Raman photofragment spectroscopy

Journal Article · Sat Feb 01 04:00:00 EST 1992 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.462083· OSTI ID:5133227

Triggs, N E; Zahedi, M; Nibler, J W ^[1]; DeBarber, P; Valentini, J J ^[2]

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1. Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 (United States)
2. Department of Chemistry, University of California at Irvine, Irvine, California 92717 (United States)

Coherent anti-Stokes Raman spectroscopy (CARS) was used to measure the vibrational--rotational {ital Q}-branch structure of the {nu}{sub 1} symmetric stretch of methyl radicals produced by 266 nm laser photolysis of methyl iodide. Spectra were recorded in both flow cells and free jet expansions at instrumental resolutions ranging from 0.25 to 0.005 cm{sup {minus}1}. Due to the high recoil velocity of the CH{sub 3} fragment, Doppler and collisional broadening of the transitions is appreciable. Even at the highest resolution such broadening of the transitions leads to interference effects among the closely spaced Raman transitions that influence both the line positions and intensities in the observed CARS spectra. The molecular parameters (cm{sup {minus}1}) obtained from the analysis are {nu}{sub 1}=3004.42(4), {alpha}{sub {ital B}1}=0.0851(8), {alpha}{sub {ital C}1}=0.0475(7), {ital D}{sub {ital N}1}{minus}{ital D}{sub {ital N}0}={minus}0.000 046(8), {ital D}{sub {ital NK}1}{minus}{ital D}{sub {ital NK}0}=0.000 083(20), and, with assumptions, {ital D}{sub {ital K}1}{minus}{ital D}{sub {ital K}0}={minus}0.000 039. These results and infrared data in the literature yield a CH bond length of 1.08378(5) A for the (1000) state and, with some assumptions, an equilibrium bond length {ital R}{sub {ital e}} of 1.076 A for this prototypic case of {ital sp}{sup 2} bonding.

• OSTI ID: 5133227
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 96:3; ISSN JCPSA; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

664100* -- Theory of Electronic Structure of Atoms & Molecules-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ALKYL RADICALS
BOND LENGTHS
CHEMICAL REACTIONS
COLLISIONS
DECOMPOSITION
DIMENSIONS
DOPPLER EFFECT
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
EQUILIBRIUM
EXCITED STATES
HALOGENATED ALIPHATIC HYDROCARBONS
IODINATED ALIPHATIC HYDROCARBONS
JETS
LASER SPECTROSCOPY
LASERS
LENGTH
METHYL IODIDE
METHYL RADICALS
MOLECULE COLLISIONS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATIONS
RADICALS
RAMAN SPECTROSCOPY
RECOILS
RESOLUTION
ROTATIONAL STATES
SPECTROSCOPY
SYMMETRY
ULTRAVIOLET RADIATION
VELOCITY
VIBRATIONAL STATES