On the use of the pseudo-diatomic model for experimental evaluation of stabilization energies of weakly bound molecular complexes

Abstract

Energias de estabilização para complexos moleculares fracamente ligados, relativas aos monomeros isolados, tem sido determinadas experimentalmente através do modelo pseudo-diatômico (PD) o qual faz uso de um potencial do tipo Lennard-Jones 6-12 (LJ), aqui denominado modelo PD-LJ. Este método utiliza da dos espectroscópicos para avaliar a profundidade do poço de potencial para sistemas fracamente ligados. Neste trabalho é mostrada uma comparação sistemática en tre valores experimentais de energias de estabilização disponíveis na literatura e calculados à nível ab in itio para uma série de complexos binários, objetivando avaliar a eficácia do modelo PD-LJ.Sta bi li za tion en er gies of weakly bound mo lec u lar com plexes, rel a tive to the iso lated mono mers con stit u ents, have been eval u ated ex per i men tally us ing the pseudo-diatomic (PD) model em ploy ing a Lennard-Jones 6-12 po ten tial (LJ), here de nom i nated the PD-LJ model. This method uses spec tro scopic data to es ti mate the po ten tial depth of weakly bound spe cies. In this work we re port a sys tem atic com par i son be tween high level ab in itio sta bi li za tion en ergy val ues and the re spec tive ex per i men tal data avail able for a se ries of bi nary com plexes, aim ing to as sess the efficaciousness of the PD-LJ model. Key words : sta bi li za tion en ergy, weakly bound com plexes, ab in itio , pseudo-diatomic model In tro duc tionThe sub ject of weakly bound mo lec u lar com plexes has at tracted the at ten tion of many experimentalists and the o reti cians and, con se quently, this re search field has grown con sid er ably over the past years. Ex per i men tal stud ies on such mo lec u lar sys tems, mainly dimeric and trimeric species, have been con ducted in the gas phase with struc tural and en ergy data be ing ob tained through the aid of in fra red (IR) and mi cro wave spectroscopies. The sam ple is usu ally pro duced in a su per sonic ex pan sion of the mix ture of the mono mers where the for ma tion of small mo lec u lar as so ci ations, mainly bi nary and ter nary com plexes, are de tected. The ex per i ments are con ducted at low tem per a ture and pres sure con di tions. Ex per i men tal in ves ti ga tions on a num ber of gas phase dimers have been ac com plished us ing pulsed-nozzle Fou rier-transform mi cro wave spec tros copy.In many cases the ge om e try of the com plex is unambiguosly de ter mined by the experimentalists. The exper i men tal de ter mi na tion of mo lec u lar prop er ties for weakly bound com plexes through spec tro scopic techniques has been well doc u mented. On the other side the o ret i cal stud ies of weakly bound spe cies have been in creas ingly re ported in the lit er a ture. Re views on the the o ret i cal ap proaches and pro gresses achieved in this field are given in Refs. 6-10. For a more recent re view of the pres ent sta tus of the o ret i cal stud ies of mo lec u lar as so ci a tions see Ref. 1. One-electron prop er ties like elec tric field gra di ent, have been found to be very sat ...