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

ALMA Capabilities for Observations of Spectral Line Emission

The Atacama Large Millimeter/submillimeter Array (ALMA) combines large collecting area and location on a high dry site to provide it with unparalleled potential for sensitive millimeter/submillimeter spectral line observations. Its wide frequency coverage, superb receivers and flexible spectrometer will ensure that its potential is met. Since the 1999 meeting on ALMA Science\cite{RefA}, the ALMA team has substantially enhanced its capability for line observations. ALMA's sensitivity increased when Japan joined the project, bringing the 16 antennas of the Atacama Compcat Array (ACA), equivalent to eight additional 12m telescopes. The first four receiver cartridges for the baseline ALMA (Japan's entry has brought two additional bands to ALMA's receiver retinue) have been accepted, with performance above the already-challenging specifications. ALMA's flexibility has increased with the enhancement of the baseline correlator with additional channels and flexibility, and with the addition of a separate correlator for the ACA. As an example of the increased flexibility, ALMA is now capable of multi-spectral-region and multi-resolution modes. With the former, one might observe e.g. four separate transitions anywhere within a 2 GHz band with a high resolution bandwidth. With the latter, one might simultaneously observe with low spectral resolution over a wide bandwidth and with high spectral resolution over a narrow bandwidth; this mode could be useful for observations of pressure-broadened lines with narrow cores, for example. Several science examples illustrate ALMA's potential for transforming millimeter and submillimeter astronomy.Comment: 6 pages, for the Proceedings of Science with ALMA: a new era for Astrophysics: International Conference, 2006 held 13 - 17 November 2006 in Madrid, Spai