Revised analysis of the structure of the v1 band of methane

A simple model to simulate the Raman spectrum of methane in the range of 2800–3040 cm−1

“…We subtracted the simulated spectra of the ν 3 band from experimental unpolarized ones to obtain pure polarized bands at different pressures (see Figure 3). The most intense ν 1 band centered at 2917 cm −1 is formed by multiple significantly overlapping lines belonging to the Q branch 45,59–61 . Despite the proximity of vibrational levels, the pressure effect on this peak is the opposite to that of the ν 3 and ν 2 + ν 4 bands.…”

“…The most intense ν 1 band centered at 2917 cm À1 is formed by multiple significantly overlapping lines belonging to the Q branch. 45,[59][60][61] Despite the proximity of vibrational levels, the pressure effect on this peak is the opposite to that of the ν 3 and ν 2 + ν 4 bands. As can be seen in Figure 3B, the ν 1 band significantly shifts towards low wavenumbers 23,27,62,63 but slightly broadens 25,[64][65][66] with increasing pressure.…”

The ro-vibrational ν2 mode spectrum of methane investigated by ultrabroadband coherent Raman spectroscopy

“…Despite the different nature of their emission, 33 SRS and CRS share the use of the driving pump and Stokes laser fields with frequency differences matching the ro-vibrational transitions of the Raman-active molecules, resulting in the emission of a coherent signal, which can be remotely detected even in harsh environments. Since the very beginning of their development, continuous-wave SRS 34,35 and CRS [36][37][38][39] have been employed to perform high-resolution measurements of the ro-vibrational Raman spectrum of CH 4 in the so-called pentad region, allowing for the assignment of individual rotational lines in the isotropic Q-branch of the symmetric C-H stretch [v 1 mode, see Fig. 1(a)].…”