TRANSITION DIPOLE MOMENT AND LINE STRENGTHS FOR THE $\nu_{2}$ FUNDAMENTAL BAND OF THE METHYL RADICAL

$^{a}$C. Yamada and E. Hirota, J.Chem. Phys. 78, (2) 669 (1983).Author Institution: INP-Greifswald; Department of Chemistry, University of CambridgeThe determination of methyl radical concentrations in terrestrial and astronomical sources using infrared spectroscopy relies on the availability of accurate line strengths and transition dipole moments. The $\nu_{2}$ fundamental of $CH_{3}$ near $606 cm^{-1}$ is particularly useful for this purpose but the current value of its transition dipole moment is uncertain by at least $20%$. We have measured the line strength of 9 Q-branch lines of the $2^{1}_{0}$ band of $CH_{3}$ from Q(1,1) to Q(12,12) using diode laser absorption spectroscopy. The method is based on following the recombination rate of methyl radicals in a pulsed discharge in tertiary butyl peroxide heavily diluted in $argon^{a}$. The translational, rotational and vibrational temperatures of the radical were precisely determined from line widths and relative line intensities in both the $\nu_{2}$ fundamental and hot bands. The new value of the transition dipole moment is $0.22 \pm 0.02$ D which is compatible with most previous measurements and calculations, and with the transition dipole moment of the $\nu_{3}$ band