Berechnung der Aktivierungsenergien für die thermische cis-trans-Isomerisierung substituierter Stilbene, Stilbazole und Stilbazolium-Salze

Die Aktivierungsenergien der thermischen cis-trans-Isome- risierung substituierter Stilbene, Stilbazole und Stilbazolium-Salze werden mittels der HMO-Methode berechnet und mit den expe- rimentellen Werten verglichen. Die Ergebnisse werden im Zusam- menhang mit dem Mechanismus der thermischen cis-trans-Isomerisierung diskutiert

Detection of a large fraction of atomic gas not associated with star-forming material in M17 SW

We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-$J$ CO lines toward the star-forming region M17SW. We mapped a 4.1pc x 4.7pc region in the [C I] 609 m$\mu$ line using the APEX telescope, as well as the CO isotopologues with the IRAM 30m telescope. We analyze the data based on velocity channel maps that are 1 km/s wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km/s ) velocity channels. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Column densities in 1 km/s channels between ~10$^{15}$ and ~10$^{17}$ cm$^{-2}$ were found for [C I]. Just ~20% of the velocity range (~40 km/s) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total gas mass estimated from the [C II] emission gives a lower limit of ~4.4x10$^3$ $M_{\odot}$. At least 64% of this mass is not associated with the star-forming material in M17SW. We also found that about 36%, 17%, and 47% of the [C II] emission is associated with the HII, HI, and H_2 regimes, respectively. Comparisons with the H41$\alpha$ line shows an ionization region mixed with the neutral and part of the molecular gas, in agreement with the clumped structure and dynamical processes at play in M17SW. These results are also relevant to extra-galactic studies in which [C II] is often used as a tracer of star-forming material.Comment: 21 pages + 6 pages of appendix, 32 figures in total, accepted for publication on A&A (10/12/2014) Relevant calibrated data cubes are available on CD

Mass Spectral Fragmentation Study of Substituted 1,3-Diphenyl- 2-pyrazolines

The electron impact induced fragmentation of twenty two 1,3- -diphenyl-2-pyrazolines mono-, di- and trisubstituted in one or in both phenyl rings was studied by deuterium labelling, high and low resolution mass spectrometry, and ion kinetic energy spectroscopy. The fragmentation patterns are discussed taking into account especially the nature of the substituent and the position of substitution. The results, compared with those for the unsubstituted compound, showed that in general the phenyl ring substitution does not affect its fragmentation. The formation of stable quinoid-type ions directs many fragmentation pathways of methoxy substituted compounds

Berechnung der Aktivierungsenergien fur die thermische cis-trans-Isomerisierung substituierter Stilbene, Stilbazole und Stilbazolium-Salze

Die Aktivierungsenergien der thermischen cis-trans-Isomerisierung substituierter Stilbene, Stilbazole und Stilbazolium-Salze werden mittels der HMO-Methode berechnet und mit den experimentellen Werten verglichen. Die Ergebnisse werden im Zusammenhang mit dem Mechanismus der thermischen cis-trans-Isomerisierung diskutiert

The Nature of the Molecular Environment within 5 pc of the Galactic Center

We present a detailed study of molecular gas in the central 10pc of the Galaxy through spectral line observations of four rotation inversion transitions of NH3 made with the VLA. Updated line widths and NH3(1,1) opacities are presented, and temperatures, column densities, and masses are derived. We examine the impact of Sgr A East on molecular material at the Galactic center and find that there is no evidence that the expansion of this shell has moved a significant amount of the 50 km/s GMC. The western streamer, however, shows strong indications that it is composed of material swept-up by the expansion of Sgr A East. Using the mass and kinematics of the western streamer, we calculate an energy of E=(2-9)x10^{51} ergs for the progenitor explosion and conclude that Sgr A East was most likely produced by a single supernova. The temperature structure of molecular gas in the central ~20pc is also analyzed in detail. We find that molecular gas has a ``two-temperature'' structure similar to that measured by Huttemeister et al. (2003a) on larger scales. The largest observed line ratios, however, cannot be understood in terms of a two-temperature model, and most likely result from absorption of NH3(3,3) emission by cool surface layers of clouds. By comparing the observed NH3 (6,6)-to-(3,3) line ratios, we disentangle three distinct molecular features within a projected distance of 2pc from Sgr A*. Gas associated with the highest line ratios shows kinematic signatures of both rotation and expansion. The southern streamer shows no significant velocity gradients and does not appear to be directly associated with either the circumnuclear disk or the nucleus. The paper concludes with a discussion of the line-of-sight arrangement of the main features in the central 10pc.Comment: 51 pages, 16 figures, accepted for publication in ApJ. Due to size limitations, some of the images have been cut from this version. A complete, color PS or PDF version can be downloaded from http://www.astro.columbia.edu/~herrnstein/NH3/paper

Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+

Using an absorption line from the metastable (J, K) = (3, 3) level of H3+ together with other lines of H3+ and CO observed along several sightlines, we have discovered a vast amount of high temperature (T ~ 250 K) and low density (n ~ 100 cm-3) gas with a large velocity dispersion in the Central Molecular Zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately three fourths of the H3+ along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H3+ located in intervening spiral arms. About half of H3+ in the CMZ has velocities near ~ - 100 km s-1 indicating that it is associated with the 180 pc radius Expanding Molecular Ring which approximately forms outer boundary of the CMZ. The other half, with velocities of ~ - 50 km s-1 and ~ 0 km s-1, is probably closer to the center. CO is not very abundant in those clouds. Hot and diffuse gas in which the (3, 3) level is populated was not detected toward several dense clouds and diffuse clouds in the Galactic disk where large column densities of colder H3+ have been reported previously. Thus the newly discovered environment appears to be unique to the CMZ. The large observed H3+ column densities in the CMZ suggests an ionization rate much higher than in the diffuse interstellar medium in the Galactic disk. Our finding that the H3+ in the CMZ is almost entirely in diffuse clouds indicates that the reported volume filling factor (f ≥ 0.1) for n ≥ 104 cm-3 clouds in the CMZ is an overestimate by at least an order of magnitude.Comment: 33 pages, 5 figures, 3 table

Molecular Tracers of the Central 12 pc of the Galactic Center

We have used the BIMA array to image the Galactic Center with a 19-pointing mosaic in HCN(1-0), HCO+(1-0), and H 42-alpha emission with 5 km/s velocity resolution and 13'' x 4'' angular resolution. The 5' field includes the circumnuclear ring (CND) and parts of the 20 and 50 km/s clouds. HCN(1-0) and HCO+ trace the CND and nearby giant molecular clouds while the H 42-alpha emission traces the ionized gas in Sgr A West. We find that the CND has a definite outer edge in HCN and HCO+ emission at ~45'' radius and appears to be composed of two or three distinct streams of molecular gas rotating around the nucleus. Outside the CND, HCN and HCO+ trace dense clumps of high-velocity gas in addition to optically thick emission from the 20 and 50 km/s clouds. A molecular ridge of compressed gas and dust, traced in NH3 emission and self-absorbed HCN and HCO+, wraps around the eastern edge of Sgr A East. Just inside this ridge are several arcs of gas which have been accelerated by the impact of Sgr A East with the 50 km/s cloud. HCN and HCO+ emission trace the extension of the northern arm of Sgr A West which appears to be an independent stream of neutral and ionized gas and dust originating outside the CND. Broad line widths and OH maser emission mark the intersection of the northern arm and the CND. Comparison to previous NH3 and 1.2mm dust observations shows that HCN and HCO+ preferentially trace the CND and are weaker tracers of the GMCs than NH3 and dust. We discuss possible scenarios for the emission mechanisms and environment at the Galactic center which could explain the differences in these images.Comment: 24 pages, including 17 figures; to appear in The Astrophysical Journa