Far infrared laser magnetic resonance of singlet methylene: Singletndash;triplet perturbations, singletndash;triplet transitions, and the singletndash;triplet splittinga)

摘要

We have observed and assigned a number of far infrared laser magnetic resonance spectra of CH2arising from rotational transitions within the lowest vibrational state of theatilde;thinsp;1A1electronic excited state and from transitions between such singlet levels and vibrationally excited levels of theXtilde;thinsp;3B1electronic ground state. The singletndash;singlet transitions are magnetically active, and the singletndash;triplet transitions have electric dipole intensity because of the spinhyphen;orbit mixing of singlet levels with vibrationally excited levels of the triplet state. By identifying four pairs of singlet and triplet levels that perturb each other we can accurately position the singlet and triplet state relative to each other and determine the singlendash;triplet energy splitting. We determine thatT0(atilde;thinsp;1A1)=3165plusmn;20 cmminus;1(9.05plusmn;0.06 kcal/mol; 0.392plusmn;0.003 eV), andTe(atilde;thinsp;1A1)=2994plusmn;30 cmminus;1(8.56plusmn;0.09 kcal/mol; 0.371plusmn;0.004 eV). A newab initiocalculation of the spinhyphen;orbit matrix element between these two states has been of assistance in assigning the levels that perturb each other and has enabled us to calculate the radiative lifetimes of the lowestorthoandparalevels of theatilde;thinsp;1A1state to be about 18 s in each case.