High resolution infrared and Raman spectroscopy of ν₂ and associated combination and hot bands of ¹³C¹²CD₂

Abstract

Infrared and Raman spectra of dideuterated acetylene containing one ¹³C atom, ¹³C¹²CD₂, have been recorded and analysed to obtain detailed information on the fundamental ν ₂ band and associated combination and hot bands. Infrared spectra were recorded at 4 × 10⁻³cm⁻¹ resolution in the region 1150−2900cm⁻¹, which contains combination and hot bands from the ground and the bending v ₄ = 1 and v ₅ = 1 states. The Q-branches of the ν ₂ fundamental and associated hot bands (ν ₂ + ν ₄ − ν ₄, ν ₂ + ν ₅ − ν ₅, ν ₂ + 2ν ₄ − 2ν ₄, ν ₂ + 2ν ₅ − 2ν ₅ and ν ₂ + ν ₄ + ν ₅ − (ν ₄ + ν ₅)) were recorded using inverse Raman spectroscopy, with an instrumental resolution of about 3 × 10⁻³cm⁻¹. In addition, the observation of the 2ν ₂ − ν ₂ Raman band was carried out populating the v ₂ = 1 state by stimulated Raman pumping. In total, 11 Raman and 9 infrared bands were analysed, involving all the l-vibrational components of the excited stretching−bending manifolds up to v _t  = v ₄ + v ₅ = 2.

A simultaneous analysis of all infrared and Raman assigned transitions has been performed on the basis of a theoretical model which takes into account the rotation and vibration l-type resonances within each vibrational manifold and the Darling−Dennison anharmonic resonance between the ν ₂ + 2ν ₄ and ν ₂ + 2ν ₅ states. The parameters obtained reproduce the assigned transition wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

Keywords:

• ¹³C¹²CD₂
• high-resolution Fourier transform infrared and Raman spectroscopy
• stimulated Raman pumping
• fundamental
• combination
• overtone
• hot bands
• global analysis

Acknowledgements

G.D.L. and L.F. acknowledge the financial support of the Università di Bologna and the Ministero dell’Istruzione dell’Università e della Ricerca (PRIN ‘Spettroscopia molecolare per la Ricerca Atmosferica e Astrochimica: Esperimento, Teoria ed Applicazioni’). D.B.P. and R.Z.M. acknowledge the financial support of the Ministry of Science and Innovation through research grant FIS2009-08069.