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2 - Theoretical Principles

Published online by Cambridge University Press:  05 June 2015

Rita Kakkar
Affiliation:
University of Delhi
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Summary

Dad I understand that light is emitted when an atom decays from an excited state to a lower energy state.

Feynman That's right.

Dad And light consists of particles called photons.

Feynman Yes.

Dad So the photon ‘particle’ must be inside the atom when it is in the excited state.

Feynman Well no.

Dad Well how do you explain that the photon comes out of the atom when it was not there in the first place.

Feynman (Physics Teacher 1969) I'm sorry. I don't know I can't explain it to you.

INTRODUCTION

As was stated in Chapter 1, spectroscopy is a study of the interaction of matter with radiation. In order to understand their mutual interaction, we must therefore characterize both radiation and matter. The starting point is quantum mechanics, because the origin of quantum mechanics was based on unexplained phenomena related to both the nature of electromagnetic radiation and that of matter. In fact, quantum mechanics owes its birth to some puzzling results of spectral and other experiments. We may say that “spectroscopy is quantum mechanics in action.” We therefore begin our study of quantum mechanics with a recapitulation of its postulates. An understanding of the postulates is also essential for our development of the time-dependent perturbation theory and also forms the basis for the connection between theory and experiment. Indeed, spectroscopy is the experimental verification of the laws of quantum mechanics.

Quantum mechanics is based on a few postulates (from the Latin postulatum), meaning a truth that does not need any further proof, because it is obvious by itself, and its success lies in the fact that no experiment till date has proved it wrong. There is no agreement of how many axioms one needs to describe the machinery of quantum mechanics; however, the six given below is an acceptable number.

Type
Chapter
Information
Atomic and Molecular Spectroscopy
Basic Concepts and Applications
, pp. 51 - 78
Publisher: Cambridge University Press
Print publication year: 2015

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  • Theoretical Principles
  • Rita Kakkar, University of Delhi
  • Book: Atomic and Molecular Spectroscopy
  • Online publication: 05 June 2015
  • Chapter DOI: https://doi.org/10.1017/CBO9781107479999.003
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  • Theoretical Principles
  • Rita Kakkar, University of Delhi
  • Book: Atomic and Molecular Spectroscopy
  • Online publication: 05 June 2015
  • Chapter DOI: https://doi.org/10.1017/CBO9781107479999.003
Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Theoretical Principles
  • Rita Kakkar, University of Delhi
  • Book: Atomic and Molecular Spectroscopy
  • Online publication: 05 June 2015
  • Chapter DOI: https://doi.org/10.1017/CBO9781107479999.003
Available formats
×