Analysis of the Near Ultraviolet Absorption Spectrum of Acetylene

摘要

The absorption spectrum of acetylene in the region 1970mdash;2470A has been photographed in the fourth and fifth orders of a twentyhyphen;onehyphen;foot grating spectrograph with absorbing paths of 0.007 to 70 mhyphen;atmos.It has been possible to extend the arguments which led King and Ingold to conclude that in the upper electronic state the molecule is bent and hasC2hsymmetry. The upper electronic state isAuor, possiblyAg.The effective moment of inertiaIaof the excited state is small, causing subhyphen;band separations of 50 to 150 cmmdash;1. These subhyphen;bands all haveP, Q,andRbranches, are well resolved, and have the appearance of bands of diatomic molecules. The following rotational constants of the upper state are derived:A0equals;12.94,thinsp;thinsp;B0equals;1.1247,thinsp;thinsp;C0equals;1.0297thinsp;cmminus;1.If the Csngbnd;H distance is assumed to be between 1.070 and 1.090A, one findsrccequals;1.388A,thinsp;thinsp;open phiCCHequals;120compfn;.Groundhyphen;state combination differences are in agreement with precise values derived from infrared data. Some new lower stateBvalues are obtained.The Osngbnd;O vibrational transition is shown to be at 42 197.69 cmmdash;1. The subhyphen;bands form ngr;4Prime; progressions and ngr;3prime; progressions. Analysis gives two upper state vibrational frequenciesngr;3lpar;CCHrpar;equals;1047.70thinsp;cmminus;1thinsp;thinsp;andthinsp;thinsp;ngr;2lpar;CCrpar;equals;1389thinsp;cmminus;1.The following lower state vibrational constants are obtained:ohgr;40equals;608.26,thinsp;thinsp;x44equals;plus;3.29,thinsp;g44equals;plus;0.17thinsp;cmminus;1.The fundamental frequency ngr;4Prime; is the sum of these constants, that is, 611.72cmmdash;1.