High resolution spectroscopy of silane with an external-cavity quantum cascade laser: Absolute line strengths of the ν3 fundamental band at 4.6μm

- We measured the line strengths of transitions of the ν3 fundamental of 28SiH4.
- We used a cw external-cavity quantum cascade laser with narrow linewidth.
- The high resolution available enabled us to resolve the tetrahedral splittings.
- We observe excellent agreement with spherical top data system predictions.
- Excellent agreement with TDS spectroscopic database for spherical top molecules.

The introduction of room temperature continuous wave external-cavity quantum cascade lasers (EC-QCLs) with narrow linewidths has greatly facilitated high resolution spectroscopy over wide spectral ranges in the mid-infrared (MIR) region. Using the wide tuning range of an EC-QCL we have measured the absolute line strengths of many P-branch transitions of the stretching dyad of the ν3 fundamental band of 28SiH4 between 2096 and 2178 cm−1. Furthermore, the high spectral resolution available has enabled us to resolve and measure representative examples of the tetrahedral splittings associated with each component of the P-branch. The positions of these components are in excellent agreement with spherical top data system (STDS) predictions and theoretical transitions from the TDS spectroscopic database for spherical top molecules. These are the first measurements of these line strengths of 28SiH4 and are an example of the applicability of high-powered, widely tunable EC-QCLs to high resolution spectroscopy.