【摘要】 本文叙述了用在NRAO 11-m望远镜上取得的b=0°,l=20°—40因,△l=3′的¹³CO J=1-0的观测资料推出的星际分子和分子云的若干物理参量的银河径向分布以及对应上述参量不同取值区的银河系各区分子云质量谱。以此和银河旋臂所作的对比分析得出:1)分子云并不示踪银河系旋臂,它们是长寿命的天体。2)大质量云或热云的分布没有集中于旋臂的倾向,小云在银河内部区域连续分布。3)云的质量谱不依赖于分子密度和云数面密度,这对云的形成的引力坍缩和碰撞生长理论提出了一个新问题。4)由银河各区质量谱导出的云的寿命对平均寿命（〈τ〉≥2×10⁹ yrs）的起伏小于20%。更多还原

【Abstract】 In this paper the data of 391 J=1—0 spectra of ¹³CO surveys, which were made with NRAO 36″ telescope and along the galactic plane from l=20.50° to 40.00° with 3″ spacings, and 665 molecular clouds synthesized by them are used to derive the galactic radial distributions of several physical parameters of molecular clouds, such as the spatially-smoothed number density of molecular hydrogen <n_H2>, the integrated emission per cloud T_A^*d_V/N, the mean peak antenna temperature measured on l-v map <T_A^*), the surface densities of total cloud number N/S, and the large, small and warm cloud number N_L/S, N_S/S and N_W/S, respectively, and the mean chord derived assuming each chord has an equal chance of being at both the near and far distances <c>_n+f. In order to obtain the mass spectra and lifetimes of molecular clouds at different regions in our Galaxy, according to the galactic radial distributions of above-mentioned physical parameters of molecular clouds, the inner galactic plane is divided into 15 annull all together （i=1—15） in terms of five classifications（see Table 1 ,and Fig. 1, a-e）, which represent different regions where the interstellar matter is either thicker or thinner, the molecular emission is either more or less. Along with the cloud ensemble （i=16）, 15 （i=6 is lacking） mass spectra and lifetimes of molecular clouds are derived for each of such regions. The comparative analyses are made between the galactic radia distributions of physical parameters and mass spectra of molecular clouds and the molecular counterparts of HI spiral arms identified by Cohen et al （1980）^[11] in their CO surveys. Our conclusions are that. 1) Molecular clouds as a whole doesn’t trace spiral arms. the result itself gives an observational evidence about molecular couds are long-lived galactic objects. 2) The distributions of massive clouds （m>10⁵M）and warm clouds (T_A^*(¹³CO)≥2.4K, m≥10^5.5M) have not shown the tendency of constraining to the spiral arms. As for clouds less massive than 10⁵M and equal to it even though in the region of minimum value of <n_H2>, the surface density of cloul number doesn’t decrease. It implies that molecular clouds are formed randomly at a considerably steady rate and independent of spiral arms to some extent. 3) There is no clear relation between mass spectra and spiral arms. The mass spectra, thereby the formation of molecular clouds are independent of the radial varieties of their physical parameters, such as the spatial density of interstellar matter, the surface density of total cloud number etc.. Therefore a new problem is put to the theories of cloud rormation of both the gravitational collapse and cloud-cloud collisions and coalescence. Becanse botb of them were established on the condition of density dependence. 4) The mean lifetime of molecular clouds <τ>≥2×10⁹ yrs is a reasonable value in the regions of inner Galaxy between R=3.5 kpc and 10 kpc. The fluctuation of the lifetime of molecular clouds derived from each mass spectrum of 14 annuli with respect to the mean value <τ> is less than 20%.更多还原