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

在太空中探测到生物分子不仅会对星际化学产生重大影响，而且还会对地球上生命的起源等其他领域产生重大影响。为了在广阔的空间中探测它们，在实验室中准确地确定它们的旋转跃迁频率是非常重要的。在澳大利亚莫纳什大学，我们使用毫米波（42 ~ 106 GHz） 33 kHz stark调制自由射流扩展光谱仪，观察到甘氨酸、丙氨酸和甘氨酸酸酐生物分子具有强吸收系数的新旋转跃迁频率。为了观察尿嘧啶和胸腺嘧啶的旋转转变，它们应该在不分解的情况下通过加热器汽化。虽然我们试图用加热器蒸发它们，并观察它们的质量和微波光谱，但它们的质量谱显示在m/z 17(w), 18(s), 28 (s), 43(m)，它们的微波光谱显示氨，水，乙烷或碳一氧，异氰酸。但未观察到m/ z112（尿嘧啶）的离子峰。因此，我们试图用该分离器观察尿嘧啶水溶液的质谱，但未能检测到m/z 112的离子峰。现在，我们寻找出现m/z112离子峰的最优条件。采用MP2/6-31G （d, p）基础水平计算尿嘧啶和胸腺嘧啶的旋转常数。尿嘧啶的A=3879.02， B=1999.23， C=1319.28 MHz；胸腺嘧啶的A=3197.72， B=1394.66， C= 976.92 MHz。由理论计算可知，尿嘧啶和胸腺嘧啶的微波谱特征为2C=ca的区间。2640和2C=ca.1954分别MHz。在找到最佳的热解条件后，我们将观察它们的微波光谱。

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.