Basis Subroutine and System Specific Parameters: Collision of an Atom with an Asymmetric Top

System subroutine: syatp

Basis subroutine: hibaastp.f

Ref. B. J. Garrison et al., J. Chem. Phys. 65, 2193 (1976); S. Green, J. Chem. Phys. 64, 3463 (1976); 67, 816 (1979).

NTERM: the number of potential surfaces involved. This parameter should equal the number of MU terms in the angular expansion of the potential.. This parameter can not be changed

NUMPOT: an index representing the particular potential used. This variable is passed to the POT subroutine

IPOTSY: cylindrical symmetry of potential. The variables (theta,phi) describing the angular expansion of the potential should be defined with the a inertial axis defined as the body-frame z axis and, if possible, the xz plane as a plane of symmetry of the molecule (in this case, POTSY = 2). If the flag IHOMO = .true., only terms with LAMBDA + MU equal to an integer multiple of IPOTSY can be included in the potential. Example: for H₂O, IPOTSY = 2

IOP: ortho/para label for molecular states of the asymmetric top. If IHOMO =.true. then

if IOP = 1: only para states included in channel expansion
if IOP = −1: only ortho states included in channel expansion

JMAX: the maximum rotational angular momentum included in the channel expansion

EMAX: the maximum energy of a state to be included in the rotational state basis

AROT, BROT, CROT: rotational constants of the asymmetric top

| j k m s > = [2(1+δ_k0)]^−1/2 [ | j k m > + s | j −k m >]

where s is the symmetry index (+1 or −1). In this basis, the asymmetric top hamiltonian block diagonalizes into 4 groups: (1) k even, s = +1, (2) k even, s = −1, (3) k odd, s = +1, and (4) k odd, s = −1.

The expansion coefficients are stored in the array c as:

c(k=0), c(k=2), ... c(k=j), for even k

c(k=1), c(k=3), ... c(k=j), for odd k

By setting BASTST=.TRUE., you can output the values of j, s, the values of the prolate and oblate projection quantum numbers [k_p and k_o], and the internal energies, as well as the expansion coefficients.

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