#### What is spectroscopy? What is it used for? Watch the video below to find out.

### Theory

A concept of Spectroscopy is resonance, which is the quality of sound and the corresponding frequency. Resonance was first used in mechanical systems, like pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. Quantum mechanical systems use resonance as a duo of an atom and an oscillatory source of energy, known as a photon. The photon's frequency can be found with the following equation:

#### E=h/nu

The energy of a photon is related to its frequency. A spectrum of the system response vs. photon frequency peaks at the resonant frequency or energy. Electron and neutrons relationship is comparable to the photon and atom, between their kinetic energy, wavelength, and frequency therefore can also excite resonant interactions.

### Research Examples

#### Example 1:

"We present screening schemes that allow for efficient, linear-scaling short-range exchange calculations employing Gaussian basis sets for both CPU and GPU architectures. The methods account for the decay introduced by the attenuated Coulomb operator in short-range hybrid density functionals. Furthermore, we discuss the implementation of short-range electron repulsion integrals on GPUs. The introduction of our screening methods allows for speedups of up to a factor 7.8 as compared to the underlying linear-scaling algorithm, while retaining full numerical control over the accuracy. With the increasing number of short-range hybrid functionals, our new schemes will allow for significant computational savings on CPU and GPU architectures."

#### Example 2:

"We compute the x-ray emission spectrum of liquid methanol, with the dynamical effects that result from the creation of the core hole included in a semiclassical way. Our method closely reproduces a fully quantum mechanical description of the dynamical effects for relevant one-dimensional models of the hydrogen-bonded methanol molecules. For the liquid, we find excellent agreement with the experimental spectrum, including the large isotope effect in the first split peak. The dynamical effects depend sensitively on the initial structure in terms of the local hydrogen-bonding (H-bonding) character: non-donor molecules contribute mainly to the high-energy peak while molecules with a strong donating H-bond contribute to the peak at lower energy. The spectrum thus reflects the initial structure mediated by the dynamical effects that are, however, seen to be crucial in order to reproduce the intensity distribution of the recently measured spectrum."

#### Example 3:

"The bleaching process in the C–F stretching mode (ν3ν3 band) of CH3F-(ortho-H2)n [n = 0 and 1] clusters in solid para-H2 was monitored using pump and probe laser spectroscopy on the C–H stretching mode (ν1ν1 and 2ν5ν5 bands). From an analysis of the depleted spectral profiles, the transition frequency and linewidth of each cluster were directly determined. The results agree with the values previously derived from a deconvolution analysis of the broadened ν1ν1/2ν5ν5 spectrum observed by FTIR spectroscopy. The complementary increase and decrease between the n = 0 and 1 components were also verified through monitoring the ν1ν1 and 2ν5ν5 bands, which suggests a closed system among the CH3F-(ortho-H2)n clusters. These observations provide experimental verification of the CH3F-(ortho-H2)n cluster model. On the other hand, a trial to observe the bleaching process by pumping the C–H stretching mode was not successful. This result may be important for understanding the dynamics of vibrational relaxation processes in CH3F-(ortho-H2)n in solid para-H2."

Credits:

Created with images by Hubble Space Telescope / ESA - "The Hubble Ultra Deep Field 2012" • geckzilla - "NGC 5033" • geckzilla - "M2-9 "Minkowski's Butterfly"" • NASA Goddard Photo and Video - "NASA's Hubble Makes One Millionth Science Observation" • geckzilla - "Hen 2-131"