Fundamentals and Principles

Question 1

Characteristics of particles

Answer 1

Mass, momentum, and position
Momentum p = m v . Also, particles have a kinetic energy = 1/2 * m * V

Question 2

De Broglie Wave function
and Non classical particles

Answer 2

p = h/λ

Small particles can behave like waves (e.g., electrons)
Waves can behave like particles (e.g., photons

When non-classical particles move in spaces less than few De Broglie wavelenghts, their energy become quantized

The possible values of energy, which a non-classical particle can have, are called energy levels.

Question 3

Bohr Condition

Answer 3

hv= E2 -E1, where E2 is the upper level, E1 is the bottom level and hv is the energy of a photon.

a non-classical particle can
«jump» from an energy level to another only if the right amount of energy is provided

Atoms can absorb or emit light, when an electron in an atom can jump from an orbit to another, and the energy difference between the two orbits is exactly equal to the photon energy (quantum transition)

Question 4

Wavefunction Ψ

Answer 4

Schroedinger differential equation: HΨ=EΨ

describes the 3d shape of the inner wave of a particle

The square of the wavefunction in a point x,y,z is related to the probability to find the particle in that point

The wavefunction of an electron in an atom (or molecule) is called orbital

Question 5

Absorption, Emission, and Scattering

Answer 5

Spectroscopic events

Absorption = when a molecule jumps from a low energetic level to a high energetic level absorbing the energy difference as a photon of right frequency

Emission = when a molecule jumps from a high energetic level to a low energetic level emitting the energy difference as a photon of right frequency

These obey the bohr condition

Scattering = when two jumps occurr: a jump up to a high level, with photon absorbtion, followed to a jump down to a different level, with photon emission

Question 6

Electronic, Vibrational, and Rotational transitions

Answer 6

Electronic transitions (change of energy of
electrons) are induced by UV/Visible photons

Vibrational transitions (change of molecular
vibration energy) is induced by IR photons

Rotational transitions (change of molecular
rotation energy) is induced by microwave photons

Question 7

Transmittance

Answer 7

The ratio between the intensity
of transmitted and incident light: T = I/Io

Question 8

Absorbance

Answer 8

Defined as Log10 * (T)

Question 9

Lambert - Beer law

Answer 9

A = ε x C

ε = molecular absorbivity, and depends on the wavelength

Absorbance is proportional to optical path and concentration of chromophores (absorbing molecules):

Question 10

Spectrum, Spectrometers, and Spectroscopies

Answer 10

A spectrum is the plot/graph of the amount of radiation emitted/absorbed/scattered by a sample as a function of frequency/wavelength/wavenumber of the emitted/absorbed/scattered radiation

A spectrometer is a device which reports the spectrum of a sample. According to the method, it can be a transmittance or reflectance spectrometer

Spectroscopies are classified according to the event or to the type of information in
absorption/emission/scattering spectroscopies or in atomic/molecular spectroscopies. Also, spectroscopies can be in
reflectance or absorbance mode. Reflectance is preferred for CH applications,although transmittance is more efficient and
requires often very small amount of samples