Molecular dissociations and bimolecular reactions have been studied by these methods.  The dissociation of NaI has been described in the kinetics section.  We will briefly describe the bimolecular reaction of HI with OCO.  Molecular beams of HI and CO₂ are produced and are made to intersect.  Weak complexes called the van der Waals complexes are formed.  In the present case, the complex is  I - H…OCO.   The H….O distance is much longer than the OH bond distance in water or alcohols.  By the use of a femtosecond pump pulse, the HI bond is broken.  The H atom now moves closer to the oxygen to form the activated complex [HOCO]*.  The probe pulse is “tuned” to a suitable frequency of the OH radical.  Using this probe, the following dissociation process can be studied

HI + OCO →  IH…OCO →  [HOCO]* →  HO + CO                                                                 (15.17)

Mass Spectrometry (Spectroscopy) does not involve transitions between energy levels.  In this method, molecular ions are generated by ionizing the molecule (M → M⁺)  The ion M⁺ is called the parent ion.  During the ionization process, the molecules get fragmented resulting in’daughter’ ions, M_i⁺. All these ions are passed through a magnetic field which separates different ions depending on  their mass/charge ratio.  Combining the Newtons law (F=ma) and the Lorentz law (F = qE + v x B) , where m is the mass, q, the charge, v, the velocity  E the electric field and B, the magnetic field, the particle’s motion as a function of time is determined by the following combined equation.

   (m/q)a = E + v x B                                                                                                           (15.18  )

A block diagram of a mass spectrometer is shown below.