Collisional Mixing of ²Π and ²Σ states of a diatomic molecule induced by a spherical atom

BASISTYPE = 4

System subroutine: sysgpi

Basis subroutine: hiba04_sysgpi.F90

Ref. M. H. Alexander and G. C. Corey, J. Chem. Phys. 84, 100 (1986); H.-J. Werner, B. Follmeg, M. H. Alexander, and D. Lemoine, ibid. 91, 5425 (1989).

The definition of the integer system dependent parameters is as follows:

• NTERM: (the number of potential surfaces involved: this should be 1 in this case). This parameter can not be changed
• NVMINS: lowest vibrational level for sigma state
• NVMAXS: higest vibrational level for sigma state
• NVMINP: lowest vibrational level for pi state
• NVMAXP: higest vibrational level for pi state
• JMIN: the minimum rotational angular momenta for each ²Π channel
• JMAX: the maximum rotational angular momenta for each ²Π channel in each spin-orbit manifold with convention omega .le. j .le. jmax+0.5
• NMIN: the minimum Hund’s case (b) rotational angular momenta for the ²Σ state

• NMAX: the maximum Hund’s case (b) rotational angular momenta for the ²Σ state

  ⚠️ JMIN, JMAX, NMIN, NMAX are defined separately for each vibrational level

• IPERT: Each vibrational Pi level ivp may be perturbed by one sigma vibrational level IVS. This level is given by ivs=ipert(ivp) (see hisysgpi)
• IGUPI: permutation inversion symmetry of ²Π electronic state
  • IGU = 1 for gerade states
  • IGU = -1 for ungerade states
• IGUSG: permutation inversion symmetry of ²Σ electronic state
  • IGU = 1 for gerade states
  • IGU = -1 for ungerade states

  ⚠️ for heteronuclear molecules both IGUPI and IGUSG should be +1

• NPARPI: number of ²Π symmetry doublets included
  • NPAR = 2 will ensure both lambda doublets
  • NPARPI = 1 just ε = 1 doublets
  • NPARPI = -1, just ε = -1 doublets

• NPARSG: number of spin doublets in ²Σ state included (NPAR = 2 will ensure both spin doublets)

• ISYMSG: if ISYM =+1, then the electronic symmetry of the ²Σ state is sigma-plus if ISYM = -1, then the electronic symmetry is sigma-minus

• ISA: s/a symmetry index, if the molecule is homonuclear (ihomo=t) then, if isa=+1 then only the s-levels (both for sigma and pi) are included in the basis, if isa=-1, then only the a-levels are included

• ISG: if isg=1 and ipi=0 then ²Σ + atom scattering

• IPI: if ipi=1 and isg=0 then ²Π + atom scattering. If isg=1 and ipi=1 then ²Π-²Σ + atom scattering