In the present lecture, you have been introduced a few additional spectroscopic methods.  Some of the equipments in ultrafast spectroscopy are so widespread that the small sample containing the molecules is a tiny intruder.  We also hardly considered the effects of electric and magnetic fields (Stark and Zeeman effects) in spectroscopy.  The methods considered here are Mossbauer spectroscopy, NQR, Raman spectroscopy, time resolved spectroscopy and Mass spectrometry.  In Mossbauer spectroscopy, there is a reabsorption of an emitted γ-ray by the sample.  The effects of Doppler broadening are negated by moving the source relative to the sample.  In NQR, there are absorptions between the energy levels which come about by the interaction of the nuclear spin (I ≥1) with the electric field gradients at the nucleus.  In Raman spectroscopy, fluctuating molecular polarizability interacts with the incident beam to give scattered light at frequencies corresponding to rotational and vibrational energy differences.  Time resolved spectroscopy uses pump probe techniques to excite a molecule (pump pulse) and then study the time evolution of the products and activated complexes through the probe pulse. In mass spectrometry (which is not traditional spectroscopy but a great analytical tool to study molecular structures) ionization of molecules and the fragments therein enable us to identify molecular structures precisely.