Point of Interest Laser Spectroscopy

The pace of development and application of rotational, vibrational, and visible-ultraviolet spectroscopy accelerated sharply immediately after World War 11. The quantum mechanical revolution was complete in physics as of the 1930s, whereas in chemistry its full effect was not manifested until a decade or so later. The quantum level understanding that then took root in chemical science generated interest, enthusiasm, and investigation in spectroscopic analysis there was a spectroscopic revolution taking place in chemistry by the middle of the twentieth century. 

In 1951, Charles H. Townes had an idea for stimulated emission of microwave radiation. He and his coworkers at Columbia University used a transition of the ammonia molecule that occurred in the microwave region of its spectrum in order to create a maser (micro-wave amplification by stimulated emission of radiation). On producing ammonia molecules in the upper state involved in the transition, the application of microwave radiation at the transition frequency caused excited state molecules to emit a photon and drop to the ground state. Since the emitted photons were at the same frequency as that of the incident radiation, the process led to an amplification of the applied radiation. 

1 Compute the frequency in Hz for electromagnetic radiation of 1,10,100,1000, and 10,000 cm t What part of the electromagnetic spectrum do these frequencies correspond to What is the energy in / of 1 mol of photons at each of these frequencies  

2 The equilibrium bond length of LiH is 1.595 A. Find the equilibrium rotational constant in cm for LiH and for the isotopic forms, LiD and LiH, taking the bond lengths to be identical. 

3 Using data in Table 9.1, calculate the band center frequency (i.e., the average of the frequency of the first P-branch and first P-branch lines) for the n = 0 1, l- 2,2- 3 and 3 4 vibrational bands of LiH. 

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