[molpro-user] D_inf_h Vs. D2h

[Terry Frankcombe]

On Tue, 2009-06-09 at 11:03 +0300, muskatel at fh.huji.ac.il wrote:
> Hi,
> 
> I am trying to do some calculations on N2 molecule.
> This molecule belongs to D_inf_h point group, but for some reason in  
> the manual there is no character table for that only for D2h.
> Also, there is a particular example for N2 molecule  given in the  
> manual using D2h.

As it says in the manual, molpro only uses Abelian point groups.
D_inf_h is not one of those.  D2h is the highest symmetry Abelian
subgroup that applies, so that's used.

> In the spectroscopic literature there are only states belonging to  
> D_inf_h for N2 (Sigma_g_+, Sigma_g_- , Pi_g_ Pi_u  etc.) and not D2h  
> (Ag, B2g, B2g etc ...)
> 
> Why is that?
> How can I go from one to the other?

You need to understand what the Sigma_g+ etc. mean and translate them
into appropriate representations in the lower symmetry group.

As I'm not a spectroscopist I don't know these symbols off by heart, so
when I need to understand them I go to this paper:  Schutte et al., Pure
& Appl. Chem. 69 (1997) 1641.  Sigma_g+ correlates with Ag.