Molecular spectroscopy : = La spectroscopie moleculaire : general and introductory lectures presented at the Fifth European Congress on Molecular Spectroscopy held in Amsterdam, The Netherlands, May 29th-June 3rd, 1961 =: conferences generales et d'initiation presentees au Cinquieme Congres Europeen de Spectroscope Moleculaire a Amsterdam, Pays-Bas, Mai 29-Juin 3, 1961 (Butterworths, 1962)