High-resolution Raman spectroscopy of n2 and associated hot bands of 13CH12CH: global analysis of the anharmonic resonances

The Raman spectrum of the 13CH12CH molecule in the region of its n2 vibrational band was recorded at a resolution of 2.6103 cm1 and analyzed. Several Q branches were observed and identified, corresponding to the n2 fundamental and the associated hot bands n2 + n4 – n4, n2 + n5 – n5, n2+2n4 – 2n4 and 2n2 – n2. The usual normal modes of vibration in acetylene, with the symmetric (n1) and antisymmetric (n3) CH stretchings, the CC stretching (n2), the degenerate trans (n4) and cis (n5) bendings were adopted. All the spectra were obtained using the experimental technique of quasi-continuous stimulated Raman spectroscopy. The fundamental n2 band and the n2 + n4 – n4 and n2 + n5 – n5 hot bands were recorded at room temperature, while n2+2n4 – 2n4 was recorded at a temperature of 355 K. Finally, the spectrum of the 2n2 – n2 band was recorded at 170 K using a Raman-Raman double resonance technique in which a stimulated Raman pumping process is used to populate a single rotational level of the v2 = 1 state, prior to the spectroscopy stage. A 15 ns delay between pump and spectroscopy is introduced to allow partial collisional relaxation of the rotational population of v2 = 1 among rotational levels. The assigned Raman transitions and several previously observed infrared bands have been simultaneously fitted in order to derive a set of deperturbed molecular parameters, including the quartic anharmonic coupling coefficients K1,255 and K3,245. The ro-vibrational pattern of the stretching and stretching-bending combination states and an accurate description of the anharmonic resonances in this molecule have been obtained.