Eur. Phys. J. D 21, 143-151 (2002)
https://doi.org/10.1140/epjd/e2002-00202-4

Intermolecular and diffusive dynamics of pure acetonitrile isotopomers studied by depolarized Rayleigh scattering and femtosecond optical kerr effect

¹ LENS, via Nello Carrara 1 and INFM Unitá di Firenze, via Giovanni Sansone 1, Polo Scientifico Universitario, Sesto F.no, 50019 Florence, Italy
² Dipartimento di Chimica, Universitá di Perugia, via Elce di Sotto 8, 06100 Perugia, Italy
³ INOA, Largo E. Fermi 6, 50125 Firenze, Italy
⁴ Dipartimento di Chimica Fisica ed Inorganica, Universitá di Bologna, viale Risorgimento 4, 40136 Bologna, Italy
⁵ INFM, Unitá di Catania, Corso Italia 57, 95100 Catania, Italy

Corresponding author: ^a foggi@colonnello.lens.unifi.it

Received: 21 July 2002
Published online: 1 October 2002

Abstract

The relaxation dynamics of pure acetonitrile isotopomers has been investigated in the temperature range 8 to 75 . The overall response of the liquid is measured either recording directly the decay of the optical Kerr signal with heterodyne detection (OHD-OKE) and Fourier transforming the depolarized Rayleigh scattering spectra (DRS). The OHD-OKE signals show a decay that can be described by a bi-exponential law. At some temperatures, stressing to a maximum level the sensitivity of the OHD-OKE experimental set-up, a damped oscillation is observed on top of the fast decay component. The two techniques provide same results with a high level of reproducibility, as far as the slow component is concerned. This latter is described by an exponential law with the time constants ranging in the interval 2.0 to 0.85 ps in the light and approximately in the same interval in the deuterated molecule. The decays are, at all temperatures, well reproduced by the extended diffusion J-model. The fast component, better observed with the OHD-OKE experiments in a restricted temperature range, has time constants ranging from 550 to 350 fs. After the subtraction of the curve due to the slower decay component, the data have also been analyzed by Fourier transforming the fast part of the decay. The spectrum then consists of a broad (approximately 80 cm^-1 wide) band centered at 50 cm^-1. This band is interpreted as the manifestation of intermolecular vibrational motions.