A Search for Interstellar CH2_2D+^+

We report on a search for Interstellar CH2D+. Four transitions occur in easily accessible portions of the spectrum; we report on emission at the frequencies of these transitions toward high column density star-forming regions. While the observations can be interpreted as being consistent with a detection of the molecule, further observations will be needed to secure that identification. The CH2D+ rotational spectrum has not been measured to high accuracy. Lines are weak, as the dipole moment induced by the inclusion of deuterium in the molecule is small. Astronomical detection is favored by observations toward strongly deuterium-fractionated sources. However, enhanced deuteration is expected to be most significant at low temperatures. The sparseness of the available spectrum and the low excitation in regions of high fractionation make secure identification of CH2D+ difficult. Nonetheless, owing to the importance of CH3+ to interstellar chemistry, and the lack of rotational transitions of that molecule owing to its planar symmetric structure, a measure of its abundance would provide key data to astrochemical models.Comment: 2 pages, 1 figure, submitted to IAU Symposium 251, Organic Matte

Constraining the Environment of CH+ Formation with CH3+ Observations

The formation of CH+ in the interstellar medium has long been an outstanding problem in chemical models. In order to probe the physical conditions of the ISM in which CH+ forms, we propose the use of CH3+ observations. The pathway to forming CH3+ begins with CH+, and a steady state analysis of CH3+ and the reaction intermediary CH2+ results in a relationship between the CH+ and CH3+ abundances. This relationship depends on the molecular hydrogen fraction, f_H2, and gas temperature, T, so observations of CH+ and CH3+ can be used to infer the properties of the gas in which both species reside. We present observations of both molecules along the diffuse cloud sight line toward Cyg OB2 No. 12. Using our computed column densities and upper limits, we put constraints on the f_H2 vs. T parameter space in which CH+ and CH3+ form. We find that average, static, diffuse molecular cloud conditions (i.e. f_H2>0.2, T~60 K) are excluded by our analysis. However, current theory suggests that non-equilibrium effects drive the reaction C+ + H_2 --> CH+ + H, endothermic by 4640 K. If we consider a higher effective temperature due to collisions between neutrals and accelerated ions, the CH3+ partition function predicts that the overall population will be spread out into several excited rotational levels. As a result, observations of more CH3+ transitions with higher signal-to-noise ratios are necessary to place any constraints on models where magnetic acceleration of ions drives the formation of CH+.Comment: 7 pages, 3 figures, 2 tables, accepted for publication in Ap

Frequency shifting of pulsed narrow-band laser light in a multipass Raman cell

A multipass cell is described which allows efficient stimulated Raman frequency shifting for low pump laser intensities and low gas pressures. The latter is important for Raman shifting of narrow-band Fourier-transform limited light pulses (Δv=75 MHz). It is shown that frequency broadening of the Raman shifted light can be largely avoided in the Dicke narrowing regime at low pressures. For 75 MHz pump pulses and an H2 density of 2.5 amagat we found a negligible broadening to 90 MHz of the stimulated Stokes light. This is far below the value of 250 MHz expected from spontaneous emission. The narrow-band Stokes pulses achieved in CO2 enabled us to measure the pressure shift coefficient (-0.71×10-2 cm-1/amagat) of this gas. It is demonstrated, for the example of benzene, that our technique provides a very practical light source for high resolution molecular spectroscopy

Mixing of the vibrational angular momentum components of multiply degenerate vibronic states of benzene by vibrational l-type resonance

The rotationally resolved spectra of the 6011002 and 6011602 vibronic transitions of benzene at low rotational temperat reported and analyzed in detail. Deperturbed spectroscopic constants for the 61102 and 61162 states are reported which reproduce the observed line positions to within experimental accuracy. The splitting of 17.9 cm−1 between the two subbands of the 6011002 transition and of 6.2 cm−1 for the 6011602 transition is found to be due to vibrational l-type resonances with matrix element 8.91 and 2.65 cm−1, respectively. These large resonances cause strong distortions of the rotational structure and mix the vibrational angular momentum substates ν6minus-or-plus sign + 2ν100 and ν6± + 2ν10±2 nearly completely and the substates ν6minus-or-plus sign + 2ν160 and ν6± + 2ν16minus-or-plus sign2 substantially. The importance of the mixing for the intramolecular vibrational redistribution (IVR) and the decay behaviour of S1 benzene is discussed

The effect of the impact of comet Shoemaker Levy‐9 on Jupiter's aurorae

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95050/1/grl8225.pd

OBSERVATION OF H3+H_{3}^{+} EMISSION IN PLANETARY ATMOSPHERES: ν2→0\nu_{2} \rightarrow 0 AND 2ν2(0)→ν22\nu_{2}(0) \rightarrow \nu_{2} IN JUPITER AND ν2→0\nu_{2} \rightarrow 0 IN SATURN

$^{1}$. L. Trafton, D. F. Lester, and K. L. Thompson, Astrophys. J. 343, L73 (1989). $^{2}$. P. Drossart, J.-P. Maillard, J. Caldwell, S. J. Kim, J. K. G. Watson, W. A. Majewski, J. Tennyson, S. Miller, S. K. Atreya, J. T. Clarke, J. H. Waite, Jr., and R. Wagener, Nature 340, 539 (1989). $^{3}$. T. Oka and T. R. Geballe, Astrophys. J. 351, L53 (1990). $^{4}$. R. Baron, R. D. Joseph, T. Owen, J. Tennyson, S. Miller, and G. E. Ballester, Nature 353, 539 (1991). $^{5}$. T. R. Geballe, M.-F. Jagod, and T. Oka, Astrophys. J. in press.Author Institution: Joint Astronomy Centre; Department of Chemistry and Department of Astronomy and Astrophysics., The University of ChicagoSince the initial observations of the $2 \mu m 2 \nu_{2}(2) \rightarrow 01.2$ and $4 \mu m \nu_{2} \rightarrow 0^{3}$ bands of $H3+$ in Jupiter, their temporal variation in the Jovian polar auroral regions has been $established.^{3,4}$ We report five transitions at $3.54 \mu m$ of the $\nu_{2} \rightarrow 0$ fundamental band of $H_{3}^{+}$ observed in emission across Jupiter. The strongest emissions occurred in the polar regions, and their intensities feel off by an order of magnitude away from the poles. Additionally, a hot band transition $2\nu_{2}(0) \rightarrow \nu_{2} (J = 9, K = 9 \rightarrow J = 8, G = 9, U = 1)$ was observed. Three transitions of the $v2$$0$ band at $3.53 \mu m$ and $3.67 \mu m$ were detected in $Saturn.^{5}$ which becomes the third planet to naturally exhibit $H_{3}^{+}$ emission. The intensity of the transition at $3.53 \mu m (J = 4, G = 3, U = -1 \rightarrow J = 3, K = 3)$ in Saturn was weaker than in Jupiter by about a factor of 130, and the total column density was $1.0 \times 10^{11} cm^{-2}$. All observations were made with the CGS4 spectrometer at the United Kingdom Infrared Telescope on Mauna Kea. Hawaii

EXTENDED ASSIGNMENT OF CH3+CH_{3}^{+}: v3v_{3} FUNDAMENTAL AND HOT BANDS

$^{1}$ M. W. Crofton, M.-F. Jagod, B. D. Rehfuss, W. A. Kreiner, and T. Oka, J. Chem. Phys. 88 , 666 (1988).Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago; Physikalisch-Chemisches, Institut der Universit\""{a}t Z\""{u}richWe have completed a high sensitivity survey of our $CH_{4}$-$H_{2}$-He, liquid-nitrogen-cooled discharge from $3300 cm^{-1}$ down to $2900 cm^{-1}$. Many of the newly observed lines have been assigned to the $v_{3}$ fundamental band of $CH_{3}^{+}$, substantially extending our previous work to higher rotational $levels.^{1}$ Other lines correspond to the $v_{2} + v_{3} \leftarrow v_{2}, v_{3} + v_{4}(l=2) \leftarrow v_{4}$ and $v_{3} + v_{4} (l=0) \leftarrow v_{4}$ hot bands, which are complicated by large Coriolis interaction due to the near degeneracy of $v_{2}$ and $v_{4}$. Their analysis is underway