A sealed glass tube contains a mixture of two noble gases at low pressure. A student records the bright-line emission spectrum and measures the wavelengths (in nm) and relative intensities (arbitrary units) of six of the strongest lines.
Observed Spectrum of the Mixture
Wavelength (nm) | Relative Intensity
───────────────┼──────────────────
388 | 0.60
402 | 0.25
447 | 1.00
468 | 0.40
587 | 0.90
616 | 0.35
For comparison, a handbook lists the following strong lines (no intensities provided):
• Helium: 388 nm, 447 nm, 468 nm, 588 nm
• Neon: 540 nm, 585 nm, 616 nm, 703 nm
• Argon: 404 nm, 436 nm, 706 nm, 738 nm
(a) Using only the wavelength information, rank the three candidate gases (helium, neon, argon) in order of likelihood of being present in the tube. Clearly reference the observed lines that influence your ranking.
(b) The student claims that the relative intensity pattern indicates the presence of both helium and neon. Evaluate this claim by discussing how source conditions and atomic transition probabilities could affect intensity measurements. Include at least two distinct physical factors in your discussion.
(c) Propose an additional experimental measurement or manipulation that would strengthen the identification of the gases beyond the qualitative comparison carried out in part (a). Explain how the proposed procedure would provide more conclusive evidence.
(d) Suppose a weak line at 540 nm is later detected at relative intensity 0.05. Reassess your ranking from part (a) in light of this new information and justify any change to the ordering.