The abundances of simple molecules are examined in terms of the time-dependent cloud evolution. The formation and destruction mechanisms of H 2 C O are reviewed. The average value of the fractional abundance of H 2 C O is derived to be in the range of 10 − 10 t o 5 × 10 − 9 . This is comparable to the observed values. The expected variations of the molecules formed from or destroyed by CO, CI, and C + whose abundances depend on the evolutionary state of the cloud are discussed.

ABSTRACT
Ⅰ. INTRODUCTION
Ⅱ. FORMATION AND DESTRUCTION MECHANISMS OF FORMALDEHYDE
Ⅲ. FRACTIONAL ABUNDANCE OF FORMALDEHYDE
Ⅳ. TIME DEPENDENT ABUNDANCES OF CO AND CI
Ⅴ. ABUNDANCES OF SIMPLE MOLECULES IN THE TIME-DEPENDENT CLOUD EVOLUTIONARY MODEL
Ⅵ. CONCLUSIONS
REFERENCES

• Y. K. MINN(National Astronomical Observatory)