Spectroscopy Questions PDF

# Questions ## 1. What are Waves? - In Diffraction and Spectroscopy, waves refer to Oscillations that propagate through space or a medium, typically electromagnetic waves (light) or (or) mechanical waves. - Diffraction occurs when waves encounter obstacles or slits, bending and spreading as a resul...

# Questions ## 1. What are Waves? - In Diffraction and Spectroscopy, waves refer to Oscillations that propagate through space or a medium, typically electromagnetic waves (light) or (or) mechanical waves. - Diffraction occurs when waves encounter obstacles or slits, bending and spreading as a result. - Spectroscopy analyzes the interaction of waves with matter to determine properties like composition, structure and energy levels. ## 2. Schrödinger Equation in a Potential Well - The Schrödinger Equation describes the quantum behavior of particles, where a Potential Well confines a particle, leading to discrete energy levels. - In a finite, infinite Potential Well, the wavefunction solutions indicate quantized states, restricting the particles' allowed energies. ## 3. What is Diffraction & Spectroscopy? - Spectroscopy is the study of how matter interacts with electromagnetic waves to analyze its composition, structure, and energy states. - Diffraction is the blending and spreading of waves when they encounter an obstacle or pass through a narrow slit, producing interference patterns. ## 4. How do we calculate the absorption coefficients? - The absorption coefficient (α) quantifies how much light or radiation a material absorbs over a given distance. - It is calculated using the Beer-Lambert Law: - α = 2.303 * A / d - Where: - α is the absorbance. - d is the path length of the material (in cm). - 2.303 converts from base 10 logarithm to natural logarithm. - For direct calculations from transmittance (T), use: - α = -ln(T) / d - Where T= I/Io is the ratio of transmitted intensity to incident intensity. ## 5. How do you find transition probability of the given level to the other level? - In Diffraction and Spectroscopy, the transition probability between two levels can be calculated using Fermi's Golden Rule: - P_i-f = (2π/ħ) * |<f|H'|i>|² * ρ(E_f) - Where: - P_i-f is the transition probability. - H' is the perturbation (interaction Hamiltonian). - <f|H'|i> is the matrix element of the interaction. - ρ(E_f) is the density of final states at energy E_f. ## 6. What decides the height of peaks/absorption coefficients? 1. Transition Dipole Moments (μ): *2(ω) α μ²μ* 2. Density of States: *<f|H'|i>* 3. Transition probability: *<f|H'|i>* 4. Concentration of Absorbing species 5. Linewidth (Broadening): - The absorption coefficient α(ω) can be modeled as: - α(ω) = N / ħ * |μ|² * ρ(E_f) * Γ - Where: - N = No. of absorbers. - Γ is the linewidth. - ρ(E_f) = density of states. ## 7. Can we do absorption in spectroscopy for a Single Crystal? - Yes, absorption spectroscopy can be performed on a single crystal, but the crystal must be oriented such that the light interacts with specific crystal planes, as the absorption properties can vary with orientation due to anisotropy. - The absorption spectrum will depend on the crystal symmetry and polarization of the incident light. ## 8. Distance between a person and wall = 100 cm, distance between points on wall = 15 cm. So what is the periodicity? - Periodicity (P) = spacing between maxima. - P can be calculated as: - P = distance between points on the wall / distance from person to wall * distance between points in the diffraction pattern ## 9. How phase related to spectroscopy? - In spectroscopy, the phase of light relates to how electromagnetic waves interact with matter, affecting coherence, interference patterns, and ability to study dynamic processes, molecular vibrations, and structural properties in materials. ## 10. Why Raman is so special? - Raman spectroscopy relies on the phase-related interactions of light with molecular vibrations. - The Raman Effect occurs when the phase and energy of scattered light shift due to inelastic scattering, providing unique insights into molecular structure, composition, and dynamics, making Raman spectroscopy a powerful analytical tool. ## 11. How does Raman tell about the bonds? - Raman reveals bond information by detecting molecular vibrations unique to each bond through inelastic light scattering. ## 12. Intensities of Stokes are higher than anti-stokes why? - Stoke lines are higher in intensity than anti-Stokes lines because, in most cases, the population of molecules in the ground state is higher, leading to more scattering at lower energy states (Stokes Shift) than at higher energy states (anti-Stokes Shift). ## 13. What leads to laser emission, and how is it beneficial? - Laser emission occurs when atom or molecules undergo stimulated emission, where an incoming photon causes the emission of a coherent photon of the same energy, phase, and direction. - It is beneficial for applications requiring highly focused, monochromatic, and coherent light, such as in communication, medicine, and manufacturing. ## 14. Why is the narrow linewidth of gas lasers and diode lasers important in the context of Raman spectroscopy? - The narrow linewidth of gas lasers and diode lasers is important in Raman spectroscopy because it provides high spectral resolution, which is crucial for distinguishing between closely spaced vibrational modes. - A narrow linewidth ensures minimal overlap between the Raman scattered light and the incident laser light, improving the sensitivity and accuracy of the spectral measurements. ## 15. How is phase connected to Raman spectrum? - Different phases have distinct vibrational modes helping us detect different phases using Raman spectroscopy. - Phase transitions in Raman spectroscopy: - When a material undergoes a phase transition, its bonding environment and molecular vibrations change. This leads to: - Shift in peak position (frequency shifts) - Changes in peak intensity - Appearance or disappearance of peaks - Broadening or narrowing - Crystalline phases have sharp-well-defined phases while amorphous phases have broader peaks due to distorted stresses. - Using the Raman effect, we can detect solid-solid, solid-liquid, and liquid-gas phase transformations. ## 16. Why do we want bond? What do we do with it? - This question seems incomplete or missing context. It doesn't make complete sense as it currently stands.