Absorption Spectrum Of Methane Research Articles

The Absorption Spectra of Methane, Carbon Dioxide, Water Vapor, and Ethylene in the Vacuum Ultraviolet

Quantitative absorption measurements were made of methane, carbon dioxide, water vapor, and ethylene at 30°C in a Cario and Schmidt-Ott vacuum fluorite spectrograph from 1400 to 2000A. Values of the atmospheric absorption coefficient, α, in the equation, I=I0 exp(—αx), ranging from two for carbon dioxide to 800 for ethylene were found. Resonance wave-lengths and oscillator strengths were calculated from absorption curves and found to be consistent with refractive index data.

Absorption spectra of methane in the near infrared

A grating spectrometer with a PbS cell for detector has been used for the measurement of the infrared absorption bands of methane in the region of 1.66 /-t. Many lines of the P, 0, and R branches of the 1.66-ju band have been observed. These are well resolved and are of the correct structure and spacing for the F2 component of 2 vz. The lines for values of / up to 10 are sharp^ showing no indication of splitting due to interaction with neighboring states or to centrifugal distortion. The rotational constants obtained for this band are B' = 5.178, £3 = 0.0346. The latter value is lower than in the vz fundamental. Other bands observed are more, complex and irregular, presumably due to mutual interaction.

The Ultraviolet Absorption of Methane

The absorption spectrum of methane from 1450A to 850A is found to be entirely continuous and all excited states up to the first ionization potential are repulsive.

The Near Infrared Absorption Spectrum of Methane

The infrared absorption spectrum of methane between 1.4\ensuremath{\mu} and 2.6\ensuremath{\mu} was obtained with an infrared spectrometer having a grating of 5000 lines to the inch. Strong bands were found in the 1.6\ensuremath{\mu} and 2.3\ensuremath{\mu} regions. The fine structure of the 2.3\ensuremath{\mu} band was resolved in the first order spectrum. The fine structure of the 1.6\ensuremath{\mu} band was resolved in the second order but not in the first order spectrum. Only at the 2.20\ensuremath{\mu} and the 1.66\ensuremath{\mu} bands could the fine structure be measured. The 2.20\ensuremath{\mu} band has spacing of 10.7 ${\mathrm{cm}}^{\ensuremath{-}1}$, giving for the value of the moment of inertia 5.17\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}40}$ c.g.s. units. The corresponding values for the 1.66\ensuremath{\mu} band are 10.4 ${\mathrm{cm}}^{\ensuremath{-}1}$ and 5.32\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}40}$ c.g.s. units. These results are quite close to the values of 9.77 ${\mathrm{cm}}^{\ensuremath{-}1}$ and 5.66\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}40}$ c.g.s. units found for the 3.31\ensuremath{\mu} band by Cooley.