Keywords: 
• OH /
• OCI /
• HOCl /
• 势能函数

Abstract: The possible ground state structures of OH, OCI and HOCl are optimized by using some methods included in Gaussian 09. Among them, the methods QCISD/6-311G（2df） and B3P86/6-311＋G（2df） are the most suitable for the calculation of OH（X2H） and OCI（X2H） the spacings between eguilibrium nuclei ROH = 0.09696 nm and Rocl = 0.1569 nm, and harmonic freguencies w（OH） = 3745.37 cm-1 and w（OCI） = 892.046 cm-1 are calculated respectively. The calculation results are in good agreement with experimental results, Each potential energy curve obtained via scanning the single point energies of OH and OCI is well fit with the four-parameter Murrell-Sorbie function, according to which spectral data and force constants are deduced. The ground state of HOCl molecule is of 2A1＇ state, and the parameters of structure are Roll = 0.0966 nm, ∠HOCl = 102.3°, w1 （a1） = 738.69 cm-1, w2 （b2） = 1260.25 cm-1, D e = 2.24 eV with QCISD（T）/D95（df, pd）. The present calculation results are in excellent agreement with the experimental values, and they are better than those given in the literature. And the force constants are calculated at the same time. The potential energy function of HOCl is derived from the many-body expansion theory. In the symmetric-stretch potential energy diagram, there is a saddle point in reaction channel H＋OCl→HOCl, and a stable HOCl molecule could be formed only when H atom crosses an energy barrier of 1.74 eV. However there is no clear energy barrier in the reaction channel Cl＋OH→HOCl, therefore a stable HOCl molecule can form easily.