Toward a global model of the interactions in low-lying states of methyl cyanide: rotational and rovibrational spectroscopy of the $v_4 = 1$ state and tentative interstellar detection of the $v_4 = v_8 = 1$ state in Sgr B2(N). (arXiv:2103.07389v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Muller_H/0/1/0/all/0/1">Holger S. P. Müller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Belloche_A/0/1/0/all/0/1">Arnaud Belloche</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lewen_F/0/1/0/all/0/1">Frank Lewen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Drouin_B/0/1/0/all/0/1">Brian J. Drouin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sung_K/0/1/0/all/0/1">Keeyoon Sung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garrod_R/0/1/0/all/0/1">Robin T. Garrod</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Menten_K/0/1/0/all/0/1">Karl M. Menten</a>
New and existing rotational spectra of methyl cyanide were analyzed to extend
the global model of low-lying vibrational states and their interactions to
$v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the
36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16,
respectively. Information on the $K$ level structure of CH$_3$CN is obtained
from IR spectra. A spectrum of $2nu_8$ around 717 cm$^{-1}$, analyzed in our
previous study, covered also the $nu_4$ band. The assignments in this band
cover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13,
respectively.
The most important interaction of $v_4=1$ appears to be with $v_8=3$, $Delta
K=0$, $Delta l=+3$, a previously characterized anharmonic resonance. We report
new analyses of interactions with $Delta K=-2$ and $Delta l=+1$, with $Delta
K=-4$ and $Delta l=-1$, and with $Delta K=-6$ and $Delta l=-3$; these four
types of interactions connect all $l$ substates of $v_8=3$ in energy to
$v_4=1$. A known $Delta K=-2$, $Delta l=+1$ interaction with $v_7=1$ was also
analyzed, and investigations of the $Delta K=+1$, $Delta l=-2$ and $Delta
K=+3$, $Delta l=0$ resonances with $v_8=2$ were improved, as were interactions
between successive states with $v_8le 3$, mainly through new $v_8le 2$
rotational data.
A preliminary single state analysis of the $v_4=v_8=1$ state was carried out
based on rotational transition frequencies and on $nu_4+nu_8-nu_8$ hot band
data. A considerable fraction of the $K$ levels was reproduced within
uncertainties in its entirety or in part, despite obvious widespread
perturbations in $v_4=v_8=1$.
We detect rotational transitions of methyl cyanide from within all
vibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot
molecular core of Sagittarius B2(N) employing the Atacama Large Millimeter
Array.
New and existing rotational spectra of methyl cyanide were analyzed to extend
the global model of low-lying vibrational states and their interactions to
$v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the
36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16,
respectively. Information on the $K$ level structure of CH$_3$CN is obtained
from IR spectra. A spectrum of $2nu_8$ around 717 cm$^{-1}$, analyzed in our
previous study, covered also the $nu_4$ band. The assignments in this band
cover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13,
respectively.
The most important interaction of $v_4=1$ appears to be with $v_8=3$, $Delta
K=0$, $Delta l=+3$, a previously characterized anharmonic resonance. We report
new analyses of interactions with $Delta K=-2$ and $Delta l=+1$, with $Delta
K=-4$ and $Delta l=-1$, and with $Delta K=-6$ and $Delta l=-3$; these four
types of interactions connect all $l$ substates of $v_8=3$ in energy to
$v_4=1$. A known $Delta K=-2$, $Delta l=+1$ interaction with $v_7=1$ was also
analyzed, and investigations of the $Delta K=+1$, $Delta l=-2$ and $Delta
K=+3$, $Delta l=0$ resonances with $v_8=2$ were improved, as were interactions
between successive states with $v_8le 3$, mainly through new $v_8le 2$
rotational data.
A preliminary single state analysis of the $v_4=v_8=1$ state was carried out
based on rotational transition frequencies and on $nu_4+nu_8-nu_8$ hot band
data. A considerable fraction of the $K$ levels was reproduced within
uncertainties in its entirety or in part, despite obvious widespread
perturbations in $v_4=v_8=1$.
We detect rotational transitions of methyl cyanide from within all
vibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot
molecular core of Sagittarius B2(N) employing the Atacama Large Millimeter
Array.
http://arxiv.org/icons/sfx.gif
