Laboratory Spectroscopy Support and Radio-Astronomical Search for Larger Interstellar Molecules, Ribonucleic Acids

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The detections of biomolecules in space would have a great impact not only on interstellar chemistry, but also on the other fields such as the origin of life on Earth. For the purpose of detecting them in spacious space, it is very important to determine accurately their rotational transitions frequencies in laboratory. In Monash University (Australia), we observed the new rotational transition frequencies with a strong absorption coefficient biomoleclues of glycine, alanine, and glycine anhydride using millimeter wave (42 to 106 GHz) 33 kHz Stark-modulated free-jet expansion spectrometer.To observe the rotational transitions of uracil and thymine, they should be vaporized without their decomposition by the heater. Although we tried to vaporize them by heater and to observe their mass and microwave spectra, their mass spectra showed at m/z 17(w), 18(s), 28 (S), 43(m), and their microwave spectra showed annmonia, water, ethane or carbon mono oxygen, and isocyanic acid. However, the ionic peak of m/z 112(uracil) was not observed. Therefore, we attempted to observe mass spectrum of water-solution of uracil using the separator, but the ionic peak of m/z 112 was not detected. Now, we search for the optimaized condition to appear the ionic peak of m/z112.We calculated the rotational constants of uracil and thymine using MP2/6-31G (d, p) basic level. It was found that A=3879.02, B=1999.23, and C=1319.28 MHz for uracil, and that A=3197.72, B=1394.66, and C= 976.92 MHz for thymine. From theoretical calculation, the characteristics of microwave spectrum of uracil and thymine show the interval of 2C=ca.2640 and 2C=ca.1954 MHz, respectively. After the optimized condition of pyrolysis may be found, we will observe their microwave spectrum.