Journal title:

The Journal of Physical Chemistry A

Abstract:

The three adiabatic potential surfaces of the Br(P2)HCN complex that correlate to the P2 ground state of the Br atom were calculated ab initio. With the aid of a geometrydependent diabatic mixing angle, also calculated ab initio, these adiabatic potential surfaces were transformed into a set of four diabatic potential surfaces required to define the full 3 x 3 matrix of diabatic potentials. Each of these diabatic potential surfaces was expanded in terms of the appropriate spherical harmonics in the atomlinear molecule Jacobi angle theta. The dependence of the expansion coefficients on the distance R between Br and the HCN center of mass and on the CH bond length was fit to an analytic form. For HCN in its equilibrium geometry, the global minimum with De = 800.4 cm(1) and Re = 6.908a(0) corresponds to a linear BrNCH geometry, with an electronic ground state of Sigma symmetry. A local minimum with De = 415.1 cm(1), Re = 8.730a(0), and a twofold degenerate Pi ground state is found for the linear BrHCN geometry. The binding energy, De, depends strongly on the CH bond length for the BrHCN complex and much less strongly for the BrNCH complex, with a longer CH bond giving stronger binding for both complexes. Spinorbit coupling was included and diabatic states were constructed that correlate to the ground P2(3/2) and excited P2(1/2) spinorbit states of the Br atom. For the ground spinorbit state with electronic angular momentum j = ((3)/(2)) the minimum in the potential for projection quantum number omega = +/((3)/(2)) coincides with the local minimum for linear BrHCN of the spinfree case. The minimum in the potential for projection quantum number omega = +/((1)/(2)) occurs for linear BrNCH but is considerably less deep than the global minimum of the spinfree case. According to the lowest spinorbit coupling included adiabatic potential the two linear isomers, BrNCH and BrHCN, are about equally stable. In the subsequent paper, we use these potentials in calculations of the rovibronic states of the BrHCN complex.
