Theory Spectroscopy

one of central concepts in spectroscopy resonance , corresponding resonant frequency. resonances first characterized in mechanical systems such pendulums. mechanical systems vibrate or oscillate experience large amplitude oscillations when driven @ resonant frequency. plot of amplitude vs. excitation frequency have peak centered @ resonance frequency. plot 1 type of spectrum, peak referred spectral line, , spectral lines have similar appearance.

in quantum mechanical systems, analogous resonance coupling of 2 quantum mechanical stationary states of 1 system, such atom, via oscillatory source of energy such photon. coupling of 2 states strongest when energy of source matches energy difference between 2 states. energy



(
e
)


{\displaystyle (e)}

of photon related frequency



(
ν
)


{\displaystyle (\nu )}





e
=
h
ν


{\displaystyle e=h\nu }





h


{\displaystyle h}

planck s constant, , spectrum of system response vs. photon frequency peak @ resonant frequency or energy. particles such electrons , neutrons have comparable relationship, de broglie relations, between kinetic energy , wavelength , frequency , therefore can excite resonant interactions.

spectra of atoms , molecules consist of series of spectral lines, each 1 representing resonance between 2 different quantum states. explanation of these series, , spectral patterns associated them, 1 of experimental enigmas drove development , acceptance of quantum mechanics. hydrogen spectral series in particular first explained rutherford-bohr quantum model of hydrogen atom. in cases spectral lines separated , distinguishable, spectral lines can overlap , appear single transition if density of energy states high enough. named series of lines include principal, sharp, diffuse , fundamental series.