DIODE LASER SPECTRA OF $CH_{3}I, NO_{2}$ AND OTHER MOLECULES AT 12-14 $\mu$m
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Date
1980
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Publisher
Ohio State University
Abstract
Perpendicular bands of several symmetric and near symmetric top molecules like $CH_{3}I, CH_{2}DI, NO_{2}$, etc., have been studied using a tunable diode laser spectrometer in the $12-14\ \mu m$ region. The limited tunability of the diode laser is compensated by its high resolution and sensitivity so that from the analysis of the Q branches alone precise band centers and rotational constants could be determined. It is known from microwave studies that $CH_{3}I$ has a large nuclear quadrupole coupling constant. The nuclear spin (I) of $5/2^{3}$ of iodine combines with J and splits the rotational levels into 2I + 1 = 6 components for J$ > 2$. Selection rules show that for J$ \simeq K, a\ ^{P}Q(J,K)$ line of the $\nu_{6}$ band is split into several components which should be resolved under Doppler-limited resolution. Such splittings were seen in the spectrum of $CH_{3}I.^{1}$ The effect of diode laser line width on the observed spectrum will also be discussed. In the case of $CH_{2}DI$ the presence of a single D atom removes the degeneracy of $\nu_{6}$ in $CH_{3}I$ and splits it into $\nu_{6}^{\prime}$ and $\nu_{6}^{\prime}$, Although the asymmetry is extremely small (x = -0.9983), spectacular asymmetry effects were observed in the $\nu^{\prime\prime}6$ band for $K^{\prime} = 0, 1, 2$ and 3. A sixth order Watson reduced Hamiltonian was used to explain these effects. In $NO_{2}$, the electron spin couples with the rotational angular momentum J of the molecule and splits it into two components Such, splittings have been observed in the $\nu_{2}$ band spectrum of $NO_{2}$ from which accurate spin-rotation interaction constants have been $determined.^{2}$
Description
$^{1}$ P. P. Das, V. Malathy Devi and K. Narahari Rao, J. Mol. Spectrosc. (in press). $^{2}$ J. M. Flaud, C. Camy-Peyret, V. Malathy Devi P. P. Das. K. Narahari Rao, J. Mol. Spectrosc. (in press).
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