Laboratory submillimeter-wave spectroscopy of interstellar deuterated molecules : evolution timescale determination of dark cloud cores

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The main subject of the present proposal is high-sensitivity submillimeter-wave spectroscopy of interstellar deuterides, aiming to estimate the chemical evolutionary age of dark cloud cores from the degree of deuterium fractionation. The following results are obtained during three years proposed.1. The present high-sensitivity submillimeter-wave spectrometer covering up to 600 GHz was improved to cover a new frequency region of 500-830 GHz, aided by the present Grant-in Aid and other sources. The new spectrometer was used to study a few interstellar deuterides given below.2. The proposed method of estimating the chemical evolutionary age of dark cloud cores from the degree of deuterium fractionation is applied to two dark cloud cores, cyanopolyyne peak and ammonia peak, of Taurus Molecular Cloud 1, using the abundance ratios between DC0^+ and HCO^+ combined with the new standard model network of gas-phase chemical reactions. The difference in deuterium fractionation between the two cor … More es is explained by a time difference in the evolutionary age of more than 10^5 yr. This is the first example of the chemical evolutionary age of dark cloud cores estimated from the degree of deuterium fractionation.3. The method proposed above is also applied to two cloud cores, the northeast NH_3 core and the southern NH_3 core, of L134N which is a typical dark cloud having no energy sources. An analysis including the degree of deuterium fractionation and C/0 depletion in cores shows that the southern core is in a more evolved stage than the northeast core. The C/0 depletion also indicates the degree of core evolution. The existence of highly fractionated NH_2D and NHD_2 recently detected at the southern core is consistent with the high C/0 depletion in the southern core.4. Two interstellar deuterides, HDC1^+ and PHD were studied with a new high-sensitivity submillimeter-wave spectrometer. Spectral patterns of PHD were very complicated due to fine and hyperfine structures of phosphorus, hydrogen and deuterium nuclei. A detailed analysis of complicated spectral lines resulted in a precise determination of the hyperfine coupling constants of phosphorus, hydrogen, and deuterium. The principal axis and principal values of the magnetic dipole coupling tensors of hydrogen in PH_2 and deuterium in PD_2 were derived from the observed values of PHD, PH_2 and PD_2. The principal axis of the hydrogen magnetic coupling tensor in PH_2 makes an angle of 2.3^0 with the PH bond. This result is one of rare cases in which a relation between the hyperfine coupling tensor and the related chemical bond is clearly indicated. Less