3. a) Multiphoton laser ionization is a process in which a high power laser indu

Question

3. a) Multiphoton laser ionization is a process in which a high power laser induces ionization of a molecule by causing it to absorb many identical photons at the same time and pool their energy to attain enough to reach the ionization potential, in other words enough to knock an electron completely off the molecule. The ionization potential of a nitrogen molecule is approximately 15.5 eV. What is the minimum number of photons from the beam of a 1054 nm high power laser that must be absorbed by a nitrogen molecule simultaneously to cause multi-photon ionization? b) For Mg atoms the ionization energy is given in our text as 738 kJ/mol. How many 1054 nm laser photons would be required to make ionization of a magnesium atom in a multiphoton event energetically feasible?

Explanation / Answer

Energy of 1054 nm photon = hc/1054x10-9*e eV
where h is plank's constant 6.67x10-34, c is peed of light = 3x108 m/sec , e is charge of elctron = 1.6x10-19 C
energy of photon = 1.17 eV

a) Number of photons needed to ionize nitrogen molecule = ioniztion potential/ energy of photon
                            = 15.5/1.17 = 13.25 or 14

b)Ionization energy of mg = 738 kj/mol
                                      = 738*1000/e*Na eV/atom ( Na is avogadro number=6x1023)
                                      = 7.7 eV/atom

Number of photos required = 7.7/1.17 = 6.6 or 7

                                    

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