UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper II covers physical chemistry.
Basic principles and applications of spectroscopy: every question, 2016 to 2025
70 parts worth 406 marks have been set on this unit in UPSC Geo-Scientist Chemistry Mains Paper II from 2016 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Electromagnetic radiation, interaction with atoms and molecules and quantization of different forms of energies. Units of frequency, wavelength and wavenumber. Condition of resonance and energy of absorption for various types of spectra; origin of atomic spectra, spectrum of hydrogen atom. Rotational spectroscopy of diatomic molecules: rigid rotor model, selection rules, spectrum, characteristic features of spectral lines. Determination of bond length, effect of isotopic substitution. Vibrational spectroscopy of diatomic molecules: simple harmonic oscillator model, selection rules and vibration spectra. Molecular vibrations, factors influencing vibrational frequencies. Overtones, anharmonicity, normal mode analysis of polyatomic molecules. Raman effect: characteristic features and conditions of Raman activity with suitable illustrations. Rotational and vibrational Raman spectra.
Notes: Rotational (microwave) and Raman spectra (full notes) · short notes
Notes: Vibrational and electronic spectra: anharmonicity and Franck–Condon (full notes) · short notes
2025
- Q1(m) Discrete levels and the resonance condition5 marks Answered
- Q1(n) Rotational activity of CO and CO₂5 marks Answered
- Q9 Are the Balmer lines equally spaced?10 marks Question only
- Q15(a) Symmetric stretch of CO₂: IR inactive, Raman active5 marks Question only
- Q15(b) Equispaced lines do not mean equispaced levels5 marks Question only
- Q15(c) B, I and r₀ of H³⁵Cl from the line spacing10 marks Question only
2024
- Q1(m) Raman effect against fluorescence and phosphorescence5 marks Answered
- Q1(n) H₂: no IR or microwave spectrum, but Raman active5 marks Answered
- Q7(b) First four Stokes lines in the rotational Raman spectrum of CO₂5 marks Question only
- Q9 Force constants of H₂⁺, D₂ and H₂10 marks Answered
- Q15(a) B, I and the bond length of H³⁵Cl10 marks Answered
2023
- Q1(m) Zero-point energy in joule and in cm⁻¹5 marks Answered
- Q1(n) Microwave activity of SF₆, CO, H₂, H₂O and CO₂5 marks Answered
- Q8 Atomic weight of ¹⁵N from the rotational lines of NO10 marks Answered
- Q15(a) Fundamental of DCl from that of HCl (same force constant)10 marks Question only
- Q15(b) Rule of mutual exclusion: CO₂ and H₂O10 marks Question only
2022
- Q1(m) Rotational constants of ¹⁴N¹⁶O and ¹⁵N¹⁶O5 marks Answered
- Q1(n) Photon–molecule interaction in rotating HCl5 marks Answered
- Q8(a) Bond lengths of H₂, N₂, O₂ from rotational Raman spectra5 marks Question only
- Q8(b) Structure of N₂O from its IR and Raman bands5 marks Question only
- Q10 Vibrational spectrum of CO₂: expected and observed10 marks Answered
- Q15(b) First overtone and hot band in IR spectra10 marks Answered
2021
- Q1(m) Microwave activity of C₂H₂, CH₃Cl, C₆H₆ and CO₂5 marks Answered
- Q1(n) Highest vibrational frequency among H₂, D₂ and HD5 marks Answered
- Q8(a) Raman spectrum: Rayleigh, Stokes and anti-Stokes lines7 marks Question only
- Q8(b) Rule of mutual exclusion and its converse3 marks Question only
- Q15(a) The J = 6 → 7 line from the J = 3 → 4 line of a rigid rotor10 marks Answered
- Q15(b) Normal modes of CS₂ and OCS; IR activity5 marks Answered
2020
- Q1(m) Hydrogen rotational spectra5 marks Answered
- Q9 Ground-level energy change for HD + DCl → D₂ + HCl10 marks Question only
- Q15(a) Rotational constant versus bond length and reduced mass5 marks Question only
- Q15(b) CO₂ bending mode: IR active, Raman inactive5 marks Question only
2019
- Q1(o) Spectral wavelength shifts5 marks Answered
- Q1(p) Bromobutane with one NMR signal5 marks Answered
- Q9(b) NMR of aromatic isomers5 marks Answered
- Q10(a) Fundamental frequency of ¹H³⁵Cl from its force constant5 marks Question only
- Q10(b) Why electronic spectra of molecules are complex5 marks Question only
- Q12(b) Symmetric carbon dioxide stretch5 marks Answered
- Q15(b) Increasing ¹H chemical shift of six compounds5 marks Question only
- Q15(c) Rotational constant; bond length of H¹²⁷I from microwave spacing10 marks Question only
2018
- Q1(o) Second Balmer line5 marks Answered
- Q1(p) Normal-mode counts5 marks Answered
- Q10(a) Stokes and anti-Stokes intensities: rotational vs vibrational Raman5 marks Question only
- Q10(b) Rotational constant from a rotational Raman spectrum5 marks Question only
- Q12(a) Infrared-active molecules5 marks Answered
- Q12(b) NMR separation at a different field5 marks Answered
- Q12(c) Trinitrobenzene proton spectra5 marks Answered
- Q12(d) Carbonyl electronic transitions5 marks Answered
2017
- Q1(h) Molar absorptivity6 marks Answered
- Q1(m) Atomic emission selection rules8 marks Answered
- Q6(a) Absorbance of liquid water for visible light2 marks Question only
- Q12(a) Hypochromic effect5 marks Answered
- Q12(c) Ethanol proton NMR10 marks Answered
- Q13(c) Nuclear spin and NMR activity5 marks Answered
- Q14(b) Moment of inertia and bond length from the J = 0→1 line10 marks Question only
2016
- Q1(o) Formaldehyde electronic transitions5 marks Answered
- Q1(p) NMR distinction of ethers5 marks Answered
- Q8(iii) Chlorine force constant4 marks Answered
- Q8(i) Harmonic-oscillator levels3 marks Answered
- Q9(a) Nuclear spin–spin coupling8 marks Answered
- Q9(b) Coupling constant2 marks Answered
- Q12(a)(i) Energy absorbed by HI3 marks Answered
- Q12(a)(ii) Counting normal modes4 marks Answered
- Q12(a)(iii) Microwave activity3 marks Answered
- Q12(b)(i) Raman-scattering lines5 marks Answered
- Q12(b)(ii) Carbon dioxide normal modes5 marks Answered
- Q13(a)(i) Rotational constant2 marks Answered
- Q13(a)(ii) Higher rotational transition2 marks Answered
- Q13(a)(iii) Information for bond length2 marks Answered
- Q13(c) Diene concentration7 marks Answered
UPSC Combined Geo-Scientist (Main) Chemistry Paper II: Model Answers 2021 to 2025
- All fifteen questions of each paper, with the question printed above its answer
- Numericals worked from formula to result with units; graphs with labelled axes
- Topic-wise weightage and a topic-wise index