Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center

Infrared absorption lines of H3+, including the metastable R(3,3)l line, have been observed toward eight bright infrared sources associated with hot and massive stars located in and between the Galactic Center Cluster and the Quintuplet Cluster 30 pc to the east. The absorption lines with high velocity dispersion arise in the Galaxy's Central Molecular Zone (CMZ) as well as in foreground spiral arms. The temperature and density of the gas in the CMZ, as determined from the relative strengths of the H3+ lines, are T=200-300K and n=50-200cm^-3. The detection of high column densities of H3+ toward all eight stars implies that this warm and diffuse gaseous environment is widespread in the CMZ. The products of the ionization rate and path length for these sight lines are 1000 and 10 times higher than in dense and diffuse clouds in the Galactic disk, respectively, indicating that the ionization rate, zeta, is not less than 10^-15 s^-1 and that L is at least on the order of 50 pc. The warm and diffuse gas is an important component of the CMZ, in addition to the three previously known gaseous environments: (1) cold molecular clouds observed by radio emission of CO and other molecules, (2) hot (T=10^4-10^6K) and highly ionized diffuse gas (n_e=10-100cm^-3) seen in radio recombination lines, far infrared atomic lines, and radio-wave scattering, and (3) ultra-hot (T=10^7-10^8K) X-ray emitting plasma. Its prevalence significantly changes the understanding of the environment of the CMZ. The sight line toward GC IRS 3 is unique in showing an additional H3+ absorption component, which is interpreted as due to either a cloud associated with circumnuclear disk or the "50 km s^-1 cloud" known from radio observations. An infrared pumping scheme is examined as a mechanism to populate the (3,3) metastable level in this cloud.Comment: 15 pages, 5 figures, 4 tables Accepted for publication in the Astrophysical Journa

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF H3+_3^+

Author Institution: Department of Chemistry, Department of Astronomy $\&$ Astrophysics,; and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637Last year we reported on the observation of 70 new rovibrational transitions of H$_3^+$ in the near-infrared and visible regions.} An additional 50 new lines have been observed since then including two hot band transitions in the near-infrared region between 10,300-12,700 cm$^{-1}$. Both liquid nitrogen and water cooled discharges were used to study the ions. The rotational temperatures of the liquid nitrogen cooled discharge is about 700 K, while the water cooled discharge has a rotational temperature around 1000 K and was used for only a few of the strong high \emph{J}$>$4 lines and the hot band transitions. These energy levels are above the barrier to linearity ($>$10,000 cm$^{-1}$), the regime in which H$_3^+$ has enough energy to sample linear configurations. A high-resolution, high-sensitivity spectrometer based on a Ti:sapphire laser and incorporating velocity modulation and phase modulation with heterodyne detection} \textbf{118}, 10890 (2003).}, was used to observe the transitions. The transitions are more than 6200 times weaker than the fundamental band. Due to the abundance of strong hydrogen Rydberg transitions, both pure hydrogen and He/H$_2$ plasmas were used to discriminate and identify the much weaker H$_3^+$ transitions. The sparsity and weakness of the lines necessitated the use of the predicted intensities and frequencies} \textbf{464}, 516 (1996).}} \textbf{101}, 189 (2003).} to focus the wavelength region of our search. The measured rovibrational energy levels will assist in the development and verification of the theoretical calculations of H$_3^+$ from first principles, which is the benchmark for \emph{ab initio} theory

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF DEUTERATED CH2+_2^+

Author Institution: Department of Chemistry, Department of Astronomy $\&$ Astrophysics,; and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637Recent observations of highly deuterated molecules such as ND$_3$ and D$_2$CO in prestellar cores and their explanation as due to the extraordinarily high deuterium fractionation of H$_3^+$ to H$_2$D$^+$, HD$_2^+$ and D$_3^+$,} \textbf{591}, L41 (2003).} have revealed the importance of observing other deuterated variants of fundamental molecular ions that also play pivotal roles in interstellar chemistry. We have launched an infrared project to study such ions systematically in order to provide their approximate rotational constants for millimeter wave spectroscopists. \vspace{2ex} We are presenting our work on the near-infrared spectroscopy of CHD$^+$ and CD$_2^+$. While our search for interstellar CH$_2^+$ based on our infrared} \textbf{153}, 738 (1992).} and near-infrared} \textbf{121}, 11527 (2004).} laboratory spectra has not been successful due to its extremely high reactivity, its detection in the future is expected in diffuse clouds since it is the intermediate between the abundant CH$^+$ and yet to be observed but very important CH$_3^+$. CH$_2^+$ and its deuterated species are also of special interest for theoretical study because of their unique intramolecular dynamics, i.e., the Renner-Teller interaction and quasi-linearity. \vspace{2ex} Using He-dominated liquid-N$_2$ cooled plasmas ($\sim$10 Torr) containing a small amount ($\sim$0.1 Torr) of CH$_4$, CH$_2$D$_2$, CD$_4$ and their mixtures, we are searching for the spectra of CD$_2^+$ and CHD$^+$ in the near-infrared from 10,500 cm$^{-1}$ to 12,500 cm$^{-1}$ with our Ti:sapphire laser spectrometer that combines velocity modulation and phase modulation with heterodyne detection for near shot-noise-limited sensitivity. Our search is based on the \textit{ab initio} calculation by Bunker, Jensen and colleagues} \textbf{225}, 33 (1997).} which predicts the $\tilde{A}(0,5,0)^1$ and $\tilde{A}(0,4,0)^1 \leftarrow \tilde{X}(0,0,0)^0$ bands of CD$_2^+$, and the $\tilde{A}(0,4,0)^1 \leftarrow \tilde{X}(0,0,0)^0$ band of CHD$^+$ as the most intense in the region

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF DEUTERATED CH2+_2^+

H. Roberts, E. Herbst, and T.J. Millar, ApJM. Rosslein, C.M. Gabrys, M.-F. Jagod, and T. Oka, J. Mol. Spectrosc.J.L. Gottfried and T. Oka, J. Chem. Phys.H. Wang, C. Morong, and T. Oka, 62 ^ndP.R. Bunker, private communications.Author Institution: Department of Chemistry, Department of Astronomy $\&$ Astrophysics; and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637Observations of highly deuterated molecules in prestellar cores and protostars in recent years have aroused new interest in deuterium ion chemistry. The widely accepted interpretation of this phenomenon as due to extraordinarily high deuterium fractionation of H$_3^+$ to H$_2$D$^+$, HD$_2^+$ and D$_3^+$} \textbf{591}, L41 (2003).} implies that deuterated variants of other fundamental molecular ions also play pivotal roles in the deuterium fractionation. Aiming at providing approximate rotational constants for millimeter wave spectroscopists to identify these deuterated species, we are continuing our project to study the laboratory spectra of the deuterated CH$_2^+$ molecular ions. CH$_2^+$ has been chosen as our first target ion because it is the intermediate between the abundant CH$^+$ and yet to be observed but very important CH$_3^+$ in the ``tree'' of interstellar chemistry. Its abundance is expected in diffuse clouds although our search for interstellar CH$_2^+$ based on our infrared} \textbf{153}, 738 (1992).} and near-infrared} \textbf{121}, 11527 (2004).} laboratory spectra has not been successful. CH$_2^+$ and its deuterated species are also of special interest for theoretical studies because of their unique intramolecular dynamics, i.e., the Renner-Teller interaction and quasi-linearity. Using He-dominated liquid-N$_2$ cooled plasmas ($\sim$10 Torr) containing a small amount ($\sim$0.1 Torr) of CD$_4$, we have measured the spectra of CD$_2^+$ in the near-infrared from 11,000 cm$^{-1}$ to 12,500 cm$^{-1}$ with our Ti:sapphire laser spectrometer that combines velocity modulation and phase modulation with heterodyne detection for near shot-noise-limited sensitivity. In this talk, we will review our analysis of the $\tilde{A}(0,5,0)^1 \leftarrow \tilde{X}(0,0,0)^0$ band, presented last year} OSU International Symposium on Molecular Spectroscopy, MJ02 (2007).} and examine the \tilde{A}(0,5,0)^0 \leftarrow \tilde{X}(0,0,0)^1$and$\tilde{A}(0,4,0)^2 \leftarrow \tilde{X}(0,0,0)^1$bands of CD$_2^+ based on the \textit{ab initio} calculations by Bunker and colleagues}. A scan for CHD^+$ is in preparation

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF He/N2_2/H2_2 POSITIVE-COLUMN PLASMAS

{M. Okumura, B. D. Rehfuss, B. M. Dinelli, M. G. Bawendi, and T. Oka, J. Chem. Phys. \textbf{90{Y. Kabbadj, T. R. Huet, D. Uy, and T. Oka, J. Mol. Spectrosc. \textbf{175{G. Osmann, P. R. Bunker, P. Jensen, and W. P. Kraemer, J. Mol. Spectrosc. \textbf{186Author Institution: Department of Chemistry, Department of Astronomy $\&$ Astrophysics,; and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637Like its isoelectronic cousins BH$_2^-$ and CH$_2$, the amidogen cation NH$_2^+$ has a quasilinear ground state $\widetilde{X}$$^3$B$_1$ with a low barrier to linearity (155 cm$^{-1}$) and metastable excited electronic states $\widetilde{a}$$^1$A$_1$ and $\widetilde{b}$$^1$B$_1$ that become degenerate ($^1\Delta$) at linearity. In addition to its theoretical interest (due to the quasilinearity and the Renner effect), NH$_2^+$ is one of the most fundamental molecular ions that exist abundantly in laboratory plasmas containing hydrogen and nitrogen. Despite this, only two high-resolution experimental detections of NH$_2^+$ have been reported (the observation of the antisymmetric N-H stretch}, 5918 (1989).} at 3360 cm$^{-1}$, and four hot bands}, 277 (1996).} from 2900-3500 cm$^{-1}$). \vspace{1em} In an attempt to observe the predicted near-infrared electronic absorption spectrum of NH$_2^+$,}, 319 (1997).} we have recently obtained new spectra of positive ions in a liquid-nitrogen-cooled positive column He/N$_2$/H$_2$ plasma. The spectra were recorded using a high-resolution, high-sensitivity spectrometer based on a Ti:sapphire laser (11,000-13,000 cm$^{-1}$) and incorporating velocity modulation, phase modulation with heterodyne detection, noise subtraction, and optical multi-passing. The observation and assignment of the spectra is complicated by the presence of thousands of lines from the $A^2\Pi_u - X^2\Sigma_g^+$ system of N$_2^+$. We will report the results of our analysis of the new spectra

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF DEUTERATED CH2+_2^+

M. Rosslein, C. M. Gabrys, M.-F. Jagod, and T. Oka, \textit{J. Mol. Spectrosc.J. L. Gottfried and T. Oka, \textit{J. Chem. Phys.H.-M. Wang, C. P. Morong, and T. Oka, 62^{ndP. R. Bunker, private communications.Author Institution: Department of Chemistry, Department of Astronomy \&$Astrophysics; and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637Laboratory spectroscopy of deuterated molecular ions is essential in understanding deuterium ion chemistry-a significant area in astrochemistry since the discovery of many extraordinarily abundant deuterated species in prestellar cores and protostars in recent years. Aiming at providing approximate rotational constants for millimeter wave spectroscopists to identify the corresponding species in space, we are measuring the near-infrared spectrum of deuterated CH$_2^+$. CH$_2^+$is the intermediate between the abundant CH$^+$and yet to be observed but very important CH$_3^+$in interstellar chemistry. Its abundance is expected in diffuse clouds although our search for interstellar CH$_2^+ based on our infrared \textbf{153}, 738 (1992).} and near-infrared \textbf{121}, 11527 (2004).} laboratory spectra has not been successful yet. CH_2^+$and its deuterated species are also of special interest for theoretical studies because of their unique intramolecular dynamics, i.e., the Renner-Teller interaction and quasi-linearity. Using He-dominated liquid-N$_2$cooled plasmas ($\sim$10 Torr) containing a small amount ($\sim$0.1 Torr) of CD$_4$, we have measured the spectra of CD$_2^+$in the near-infrared from 11,000 cm$^{-1}$to 12,500 cm$^{-1}$with our Ti:sapphire laser spectrometer that combines velocity modulation and phase modulation with heterodyne detection for near shot-noise-limited sensitivity. The$\tilde{A}(0,5,0)^1 \leftarrow \tilde{X}(0,0,0)^0$,$\tilde{A}(0,5,0)^0 \leftarrow \tilde{X}(0,0,0)^1$and$\tilde{A}(0,4,0)^2 \leftarrow \tilde{X}(0,0,0)^1$bands of CD$_2^+$have been identified and analyzed so far$, 63$^{rd}$ OSU International Symposium on Molecular Spectroscopy, MJ02 (2007) and WG04 (2008).}. Currently a scan for CHD$^+$ using CH$_2$D$_2$ gas is underway. The spectrum will be discussed in comparison with the theoretical predictions by Bunker and colleagues

A SEARCH FOR INTERSTELLAR H2_2DO+^+

T. Furuya, S. Saito, & M. Araki, J. Chem. Phys. 127, 244314 (2007)T. Araki & S. Saito, J. Chem. Phys. 128, 034311 (2008)Author Institution: Department of Chemistry, University of Chicago; Research Center for Development of Far-Infrared Region, Fukui University, Fukui, Japan; Caltech Submillimeter Observatory; Department of Astronomy and Astrophysics, and Department of Chemistry, University of ChicagoThe recent laboratory discoveries of submillimeter wave spectra of deuterated hydronium ions, H$_2$DO$^+$} and HD$_2$O$^+$,} have opened up the possibility to search for these fundamental deuterated molecular ions in dense clouds where deuterium fractionation occur efficiently. We have used the Caltech Submillimeter Observatory to search for the 0$_{00}^+$~$\rightarrow$~1$_{10}^+$ transition at 673.257007 GHz in IRAS16293A and Oph D. So far the freezing of CO and N$_2$ has been the main issue of the depletion and deuterium fractionation, but this work adds new information on depletion and deuteration chemistry of O and O$_2$. Our observational results and analyses will be presented