FT-IR data domains — what does the instrument record? An FT-IR spectrometer natively records the measured signal in which domain before applying a Fourier transform to obtain the spectrum?

Introduction / Context:
Fourier-transform infrared (FT-IR) spectroscopy acquires an interferogram produced by a Michelson interferometer. This raw signal is a function of mirror position or time and must be mathematically transformed to reveal absorption intensity versus frequency (or wavenumber). Recognizing the native acquisition domain clarifies why digital processing is integral to FT-IR.

Given Data / Assumptions:

• FT-IR uses a moving mirror to vary optical path difference continuously.
• The detector measures intensity changes as a function of time (or path difference).
• A computational Fourier transform converts the interferogram to the frequency (wavenumber) spectrum.

Concept / Approach:

The recorded interferogram encodes all spectral components through interference. Only after transforming from the time (or optical delay) domain does the familiar absorbance vs. wavenumber plot emerge. Therefore, the instrument records in the time domain and later presents results in the frequency/wavenumber domain.

Step-by-Step Solution:

Verification / Alternative check:

Central burst at zero path difference and apodization steps in software confirm time-domain acquisition. Resolution correlates with maximum optical path difference, not slit width as in dispersive instruments.

Why Other Options Are Wrong:

Option B confuses the processed domain with the recorded one. Option C is incorrect because acquisition and display occur sequentially, not simultaneously. Option E is a frequency-domain representation, obtained post-transform. “None” is unnecessary.

Common Pitfalls:

Assuming the detector directly measures absorbance vs. wavenumber; overlooking phase correction, apodization, and zero-filling steps in digital processing.

Final Answer:

Time domain