dc.creator Tanaka, Keiichi en_US dc.creator Harada, Kensuke en_US dc.creator Oka, Takeshi en_US dc.date.accessioned 2013-07-16T21:43:06Z dc.date.available 2013-07-16T21:43:06Z dc.date.issued 2013 en_US dc.identifier 2013-WF-01 en_US dc.identifier.uri http://hdl.handle.net/1811/55466 dc.description Author Institution: Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 30010, TAIWAN and Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka, 812-8581 JAPAN; Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka, 812-8581 JAPAN; Department of Astronomy and Astrophysics and Department of Chemistry, the Enrico Fermi Institute, the University of Chicago, Chicago, Illinois, 60637, USA en_US dc.description.abstract Nuclear spin conversion interaction of the water ion, H$_2$O$^+$, has been studied to derive the spontaneous emission lifetime between the {\em ortho}- and {\em para}-levels. The H$_2$O$^+$ ion is a radical with $^2 B _1$ electronic ground state and the off-diagonal electron spin-nuclear spin interaction term, $T_{ab} (S_a\Delta I_b + S_b\Delta I_a)$, connects {\em para} and {\em ortho} levels, because $\Delta \mbox{\boldmath$I$} = \mbox{\boldmath$I$}_1 - \mbox{\boldmath$I$}_2$ has nonvanishing matrix elements between $I = 0$ and 1. The $T_{ab}$ coupling constant, derived by an $ab~initio$ calculation in MRD-CI/Bk level to be 72 MHz, is larger than that of H$_2$O by 4 orders of magnitude, makes the $ortho$ to $para$ conversion of H$_2$O$^+$ faster than that of H$_2$O by 8 orders of magnitude and possibly competitive with other astrophysical processes. Last year we reported {\em ortho} and {\em para} coupling channels below 900 cm$^{-1}$ caused by accidental near degeneracy of rotational levels. MG06, 2012.} For example, hyperfine components of the 4$_{2,2}$($o$) and 3$_{3,0}$($p$) levels mix each other by 1.2 x 10$^{-3}$ due to the near degeneracy ($\Delta E$ = 0.417 cm$^{-1}$), but the lower lying 1$_{0,1}$($p$) and 1$_{1,1}$($o$) levels mix only by 8.9 x 10$^{-5}$ because of their large separation ($\Delta E$ = 16.27 cm$^{-1}$). In the present study, we solved the radiative rate equations including all the rotational levels below 900 cm$^{-1}$ to give the {\em o}-{\em p} conversion lifetime to be 0.451, 3.27, 398 and 910 years for the equilibrium $o/p$ ratio of 3.00, 3.00, 4.52, and 406 when the radiation temperature $T_r$ is 100, 60, 20 and 5 K. These results qualitatively help to understand the observed high $o$/$p$ ratio of 4.8 $\pm$ 0.5 (corresponding to the nuclear spin temperature of 21 K) toward Sgr B2, \textbf{521}, L11 (2010).} but they are too slow to compete with the reaction by collision unless the number of density of H$_2$ in the region is very low ($n\sim$1 cm$^{-3}$) or the radiative temperature is very high ($T_r >$ 50K). , $in~press$.} en_US dc.language.iso en en_US dc.publisher Ohio State University en_US dc.title RADIATIVE LIFETIME FOR NUCLEAR SPIN CONVERSION OF WATER-ION, H$_2$O$^+$ en_US dc.type Article en_US dc.type Image en_US dc.type Presentation en_US
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