Vibrational spectra and relaxation of benzonitrile and its clusters using time-resolved stimulated Raman-UV double resonance spectroscopy

Abstract

were observed by stimulated Raman-UV double resonance spectroscopy. Cluster structures were determined on the basis of the observed vibrational spectra, rotational contour analyses of the high resolution S 1 -S 0 electronic spectra and ab initio molecular orbital calculations with the HF/6-31G(d,p) basis set. It was found that the types of the cluster structures are classified into three groups. (1) The clusters with H 2 O, CH 3 OH and CH 3 CN represent the 'side'-type structure, in which the intermolecular bond is formed in the phenyl plane of benzonitrile, and the benzonitrile dimer also belongs to this structure. (2) The clusters with Ar and CCl 4 form the 'on-top'-type structure, where Ar or CCl 4 is located above the phenyl plane. (3) The clusters with CHCl 3 and CHF 3 have the 'linear'type structure, in which these molecules are located at the N end of the CN group of benzonitrile. The rate constants of the vibrational relaxation for these clusters occurring after the Raman excitation to their n 12 vibrations were also observed. It was found that different rate constants are associated with the different types of cluster structures. That is, the 12 1 levels of the 'side'-type clusters relax much faster than those of other types of the clusters. The results represent a clear indication that the anharmonic coupling between n 12 and intermolecular vibrations are much larger in the 'side'-type clusters than others.

Mode dependent intracluster vibrational energy redistribution rate in size-selected benzonitrile–(CHCl3)n=1–3 clusters

“…18,19 In the present work, we used two stimulated Raman pumping schemes depending on the energies of the vibrational levels. For the vibrations with their energies higher than 700 cm Ϫ1 , the lasers for stimulated Raman pumping were the second harmonic of an injection seeded Nd:YAG laser ͑Spectra Physics GCR-230-10͒ and the Nd:YAG laser pumped dye laser ͑Continuum ND 6000͒.…”

“…This spectroscopy was first developed by Owyoung et al, [11][12][13] and was later modified to Raman dip spectroscopy with either ionization [14][15][16][17] or fluorescence detection. 18,19 Using this technique, many Raman active vibrations were observed and they were used for the determination of cluster structures.…”

“…18 Very recently, we investigated IVR of the in-plane 12 1 mode ͑1000 cm Ϫ1 ͒ of BN, and its clusters, such as BN-͑H 2 O) 1 , BN-͑CH 3 OH) 1 , BN-͑CH 3 CN) 1 , BN dimer, BN-͑CHCl 3 ) 1 , BN-͑CHF 3 ) 1 , BN-͑CCl 4 ) 1 , and BN-͑Ar) 1 , by time-resolved stimulated Raman-UV double resonance spectroscopy. 19 We found that the IVR rate constant is very sensitive to the cluster structure, and concluded that anharmonic coupling between mode a͒ Authors to whom correspondence should be addressed. 12 and intermolecular vibrational modes is quite large for the cluster having a ''side'' structure.…”

Excitonic Splitting, Delocalization, and Vibronic Quenching in the Benzonitrile Dimer

“…18 The S 0 state was determined to be C 2h symmetric, in agreement with earlier MP2/6-31G(d,p) ab initio calculations. 18,38 Schmitt et al found the excited state structure to be asymmetric and proposed that the excitation is localized on one of the BN monomers, supported by CIS calculations which also predict a nonsymmetric structure. 18 Pratt and co-workers 19 have also reported high-resolution LIF spectra of (BN) 2 , together with a structural analysis that is in agreement with that of results of Meerts and co-workers.…”

“…The (BN) 2 S 0 state geometry was optimized using the SCS-MP2 39 and SCS-CC2 40 methods with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. Both optimizations yielded a C 2h symmetric structure, in agreement with earlier MP2 calculations with smaller basis sets, 38 and with the S 0 state rotational constants determined by the Schmitt and Pratt groups. 18,19 S 0 state normal-mode vibrational calculations were performed at the SCS-MP2/augcc-pVDZ level.…”