ON THE INITIAL EXCITATION TEMPERATURE OF INTERSTELLAR $H_{2}CO$ MOLECULES

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1970

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Ohio State University

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An attempt is made at explaining the anomalously low rotational temperature, T = 1.8$^\circ K$. of interstellar $H_{2}CO$ observed by Plamer et. $al.^{1}$ It is shown that, because of the rigorous dipole selection rules, the molecules are “adiabatically cooled” as they make transitions to lower levels by spontaneous emission. If a Boltzmanniten rotational distribution is assumed at the time of formation, the initial excitation temperature is given by $kT_{e} = 2h\bar{B}$, regardless of the temperature of formation.

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$^{1}$P. Palmer. B. Zuckerman, D. Buhl and L. E. Snyder, Ap. J. 158, L147 (1969).""
Author Institution: Division of Physics, National Research Council

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