Forbidden Rotational Transitions And Astrophysics

Oka, Takeshi

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https://hdl.handle.net/2142/116758 Copy

Description

Title

Forbidden Rotational Transitions And Astrophysics

Author(s)

Oka, Takeshi

Issue Date

2022-06-23

Keyword(s)

Astronomy

Abstract

When I read Townes and Schawlow's textbook as a beginning student, I was puzzled by the symmetric top selection rule $\mathit{\Delta}K$ = 0, because this rule corresponds to cylindrical symmetry $\mathit{C}_\infty$; applying it to NH$_3$ with $\mathit{C}_3$ symmetry cannot be right. At that time, however, I did not pursue how this wrong rule affect the actual spectrum. 10 years later interstellar NH$_3$ was discovered by Townes’ group. When I read the discoverers’ claim that lifetimes of ($\mathit{J}, \mathit{K}$) = (2,2) and (3,3) metastable levels are “longer than the lifetime of the Universe”, it was obvious that this wrong statement resulted from the wrong $\mathit{\Delta}K$ = 0 selection rule. Accurate theory\footnote{T. Oka, F.O. Shimiza, T. Shimizu, J.K.G. Watson, ApJ 165, L15 (1971)} gave the life times of the (2,2) and (3,3) metastable levels to be 230 years and 44 years, respectively, 10$^8$ times shorter than the lifetime of the Universe. The theory also predicted $\mathit{\Delta}k$ = $\pm{3}$ pure rotational transitions which were observed for PH$_3$, PD$_3$ and AsH$_3$\footnote{F.Y. Chu, T. Oka, J. Chem. Phys. 60, 4612 (1974)} $\vspace{1mm}$ In this paper\footnote{T. Oka, J. Mol. Spectrosc. 379, 111482 (2021)} I calculate spontaneous emission via forbidden transitions for astrophysically important symmetric tops; oblate tops NH$_3$, H$_3$O$^+$, H$_3^+$, and prolate tops CH$_3$CN. These calculations are preparations for future analyses of ther thermalization.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116758&&

DOI

https://doi.org/10.15278/isms.2022.RN04

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Copyright 2022 held by the authors

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