Using the Agilent Cary 670 FTIR Spectrometer to observe rotational and isotopic bands in CO through high resolution FTIR Spectroscopy

Importance of the Topic

High-resolution FTIR spectroscopy enables detailed analysis of rotational-vibrational structures and weak isotopic bands in gas-phase molecules. Such capability is essential for precise isotopic measurements, atmospheric monitoring, and fundamental molecular research.

Objectives and Study Overview

This study evaluates the performance of the Agilent Cary 670 FTIR spectrometer in resolving fine rotational and isotopic features of atmospheric carbon monoxide. The goals include assessing spectral resolution, wavelength accuracy, precision, and speed of acquisition for low-abundance isotopic species.

Methodology and Instrumentation

Experiments were conducted on an Agilent Cary 670 FTIR spectrometer purged with nitrogen, using a CO gas cell (10 cm, KBr windows) at 4 Torr. Key parameters:

• Detector: MCT narrow band (25 kHz speed, 17.4 kHz filter)
• Source: Mid-IR with retro-reflector and AC power
• Resolution: 0.09 cm⁻¹; aperture: 0.10 cm⁻¹
• Scans: 4 sample, 4 background
• Apodization: boxcar; zero filling factor: 16; UDR: 2

Results and Discussion

Spectra between 2250 and 2000 cm⁻¹ revealed well-resolved P and R branches of C¹²O¹⁶ at 2143.3 cm⁻¹. Isotopic variants C¹³O¹⁶ and C¹²O¹⁸ appeared at 2095.7 cm⁻¹ and 2092.1 cm⁻¹, respectively. Wavelength accuracy was within 0.001 cm⁻¹ of HITRAN reference values; precision better than 0.001 cm⁻¹. Spectral resolution (FWHM) for R-5 to R-7 transitions was below 0.06 cm⁻¹, all achieved in a 40-second acquisition.

Benefits and Practical Applications

The Cary 670’s large collection optics, stable retro-reflected source, and air-bearing interferometer deliver high signal-to-noise at fine resolution with fast acquisition. Applications include atmospheric CO monitoring, process analytics, and high-resolution molecular spectroscopy.

Conclusion

The Agilent Cary 670 FTIR spectrometer achieves sub-0.06 cm⁻¹ resolution, exceptional wavelength accuracy and precision, and rapid detection of weak isotopic bands, confirming its suitability for high-resolution gas-phase studies.

Future Trends and Applications

Ongoing FTIR advancements will enhance sensitivity and speed, enabling real-time isotopic tracking in environmental, industrial, and research contexts. Integration with automated sampling and chemometrics will broaden its analytical impact.

Reference

1. Rao KN and Mathews CW. Molecular Spectroscopy: Modern Research. Academic Press, New York, 1972.
2. Rothman LS et al. The HITRAN 2004 molecular spectroscopic database. J Quant Spectrosc Radiat Transf. 96(2):241-250.