Optical Spectroscopy in Emission Measurements

The energy of molecules is the sum of translational, rotational, vibrational and electronic energies: <m:math display='block'> <m:mrow> <m:msub> <m:mi>E</m:mi> <m:mrow> <m:mtext>mol</m:mtext> </m:mrow> </m:msub> <m:mtext>&#x00A0;=&#x00A0;</m:mtext><m:msub> <m:mi>E</m:mi> <m:mrow> <m:mtext>trans</m:mtext> </m:mrow> </m:msub> <m:mtext>&#x00A0;+&#x00A0;</m:mtext><m:msub> <m:mi>E</m:mi> <m:mrow> <m:mtext>rot</m:mtext> </m:mrow> </m:msub> <m:mtext>&#x00A0;+&#x00A0;</m:mtext><m:msub> <m:mi>E</m:mi> <m:mrow> <m:mtext>vib</m:mtext> </m:mrow> </m:msub> <m:mtext>&#x00A0;+&#x00A0;</m:mtext><m:msub> <m:mi>E</m:mi> <m:mrow> <m:mtext>el</m:mtext> </m:mrow> </m:msub> </m:mrow> </m:math>$$ {E_{{\text{mol}}}}{\text{ = }}{E_{{\text{trans}}}}{\text{ + }}{E_{{\text{rot}}}}{\text{ + }}{E_{{\text{vib}}}}{\text{ + }}{E_{{\text{el}}}} $$ From the point of view of the molecular spectra, translational energy E_trans is not of considerable importance, and can be neglected [101]. Rotational energy can have some significance, above all in small molecules in a gaseous state, which can rotate relatively freely.