MILLIMETER-WAVE SPECTROSCOPY OF TRANSIENT SPECIES IN SUPERSONIC JET
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Date
2008
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Ohio State University
Abstract
Submillimeter-wave absorption spectroscopy has been applied to observe transient species produced in the supersonic jet expansion with the UV laser photolysis, such as vinyl }\underline{\textbf{120}}~3604, (2004).}, FeCO }\underline{\textbf{106}} 6820, (1997).}, CoCO, CoNO, and FeNO. \par ~~~For vinyl, the proton tunneling-rotation transitions, as well as the pure rotational transitions, have been observed for the H$_2$CCH, H$_2$CCD and D$_2$CCD isotopic species to determine tunneling splitting $\Delta E_0$ and the potential barrier height $h$ for the proton (H/D) tunneling motion. Although these isotopic species have very different values for the tunneling splitting $\Delta E_0$ (16.185, 1.187 and 0.770 GHz), they have almost the same barrier heights $h$ of 1580, 1520, and 1549 cm$^{-1}$. As for the HDCCH species, the pure rotational transitions (both $a$- and $b$-types) of only one isomer ($cis$-HDCCH:D $cis$ to the unpaired electron) were observed in the jet cooled condition, but no lines for the $trans$-form nor $cis$-$trans$ tunneling transitions were detected suggesting HDCCH has $cis$- and $trans$-isomers. The difference in zero point energy between the $cis$- and $trans$-HDCCH isomers is calculated to be 32 cm$^{-1}$ with the CCSD(T)/aug-cc-pVTZ level $ab~initio$ calculation to support the present result. We also observed the large off-diagonal ($\Delta I=\pm$1) hyperfine interaction constants for H$_2$CCD which causes the nuclear spin conversion between the ortho ($I_{\beta}$=1) and para ($I_{\beta}$=0) H$_2$CCD. \par ~~~The jet cooled FeCO, CoCO, FeNO, CoNO, and Co(CO)(NO) radicals were produced in a supersonic jet expansion by excimer laser photolysis of Fe(CO)$_5$, Co(CO)$_3$NO and Fe(CO)$_2$(NO)$_2$ to observe the rotational lines. The molecular structures of FeCO, CoCO, CoNO and FeNO, for example, were confirmed to be linear with their electronic ground states of $^3\Sigma^-$, $^2\Delta_i$, $^1\Sigma^+$, and $^2\Delta_i$ as suggested by high level $ab~initio$ calculations. \par ~~~The setup was also used to observe the internal rotation transitions of the He-HCN }\underline{\textbf{117}}~7041, (2002).}, H$_2$-HCN, Ne-HCN, Ar-HCN, and H$_2$-H$_2$O complexes in the SMMW range between 60 and 360 GHz. The potential energy surfaces calculated by CCSD(T) $ab~initio$ calculation were improved to explain the experimental results to the microwave accuracy.
Description
K. Tanaka, M. Toshimitsu, K. Harada, T. Tanaka, J. Chem. Phys. K. Tanaka, M. Shirasaka, T. Tanaka, J. Chem. Phys. K. Harada, K. Tanaka, T. Tanaka, S. Nanbu, M. Aoyagi, J. Chem. Phys.
Author Institution: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashiku; Fukuoka 812-8581, Japan
Author Institution: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashiku; Fukuoka 812-8581, Japan