In contrast, the barrier separating coronene and the (5,7)-ring defected coronene corresponds to a Stone-Wales-transition structure, see also Fig. \[Entstehung.fig\].[]{data-label="trans_scheme.fig"}](Transition_scheme.eps){width="8.8cm"}

  -------------- --------------- --------------------------- ---------------
     species                            energy \[au\]        
                    $q = -1$               $q = 0$              $q = +1$
     coronene     $-920.70323$          $-920.702546$         $-920.452811$
   755-coronene   $-920.64816$          $-920.604581$         $-920.360825$
      pyrene      $-614.974253$         $-614.977292$         $-614.725558$
   7755-pyrene    $-614.90863$          $-614.892064$         $-614.651359$
                                  $\bigtriangleup$ E \[eV\]  
                    $q = -1$               $q = 0$              $q = +1$
     coronene                                                
   755-coronene      $1.50$                $2.67$                $2.50$
      pyrene                                                 
   7755-pyrene       $1.79$                $2.32$                $2.02$
  -------------- --------------- --------------------------- ---------------

  : Ground state energies and energy differences for neutral (q=0), anionic (q=-1) and cationic (q=+1) species.[]{data-label="energies"}

  -------------- -------------------------- --------------------------
     species      ionization energy \[eV\]   electron affinity \[eV\]
                          $q = 0$                    $q = 0$
     coronene              $6.80$                     $0.02$
   755-coronene            $6.63$                     $1.19$
      pyrene               $6.85$                    $(0.14)$
   7755-pyrene             $6.55$                     $0.45$
  -------------- -------------------------- --------------------------

  : Adiabatic ionization energies and electron affinities.[]{data-label="ioni"}

Discussion
==========

Formation
---------

![image](entstehungneu.eps)

The environment of carbon rich AGB stars seems to be the perfect place for PAH formation (Allamandola et al. [@alla]). One of the most important molecules in carbon-rich environments is $C_{2}H_{2}$, which is presumably the parent molecule in PAH formation (Allamandola et al. [@alla]). A detailed study on the growth of carbon molecules was done by Whitesides & Frenklach ([@white]), where they also 