Modern infrared (IR) spectroscopy acquisition: why can contemporary instruments record spectra rapidly compared with older, scanning IR instruments?

Introduction / Context:
Fourier transform infrared (FT-IR) spectrometers revolutionized IR analysis by replacing slow wavelength scanning with rapid, multiplex data collection. Understanding this principle explains their speed, signal-to-noise, and wavelength accuracy advantages.

Given Data / Assumptions:

• FT-IR uses a Michelson interferometer to generate an interferogram.
• A Fourier transform converts the time-domain interferogram into a frequency-domain spectrum.
• All wavelengths are measured simultaneously (Felgett’s multiplex advantage).

Concept / Approach:
Rather than scanning one wavelength at a time with dispersive optics, FT-IR captures combined information from all wavenumbers in a single measurement, improving speed and sensitivity, especially with signal averaging and stable lasers for wavenumber calibration.

Step-by-Step Solution:
Interference signal recorded as mirror moves → interferogram.Apply Fourier transform → spectrum with intensities across wavenumbers.Benefit: faster acquisition and improved S/N per unit time.Therefore, option a is correct.

Verification / Alternative check:
Benchmark comparisons show FT-IR acquiring full spectra in seconds versus minutes for older dispersive instruments, with higher resolution consistency.

Why Other Options Are Wrong:
Light speed (b) is a constant; option c is false since IR sources remain broadband; option e is unrelated to acquisition speed.

Common Pitfalls:
Confusing multiplex with throughput advantage (Jacquinot); both help, but multiplex is central to speed.

Final Answer:
A Fourier transform approach measures all wavelengths simultaneously (multiplex advantage).