Unimolecular dynamics from kinetic energy release distributions. V. How does the efficiency of phase space sampling vary with internal energy?

Abstract

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions ͑KERDs͒ for the C 2 H 3 Br ϩ →͓C 2 H 3 ͔ ϩ ϩBr dissociation as a function of internal energy. The KERDs obtained by dissociative photoionization using the He͑I͒, Ne͑I͒, and Ar͑II͒ resonance lines were analyzed by the maximum entropy method and were found to be well described by introducing a single dynamical constraint, namely the relative translational momentum of the fragments. Ab initio calculations reveal the highly fluxional character of the C 2 H 3 ϩ ion. As the energy increases, several vibrational modes are converted in turn into large-amplitude motions. Our main result is that, upon increasing internal energy, the fraction of phase space sampled by the pair of dissociating fragments is shown to first decrease, pass through a shallow minimum around 75%, and then increase again, reaching almost 100% at high internal energies ͑8 eV͒. This behavior at high internal energies is interpreted as resulting from the conjugated effect of intramolecular vibrational redistribution ͑IVR͒ and radiationless transitions among potential energy surfaces. Our findings are consistent with the coincidence data of Miller and Baer, reanalyzed here, and with the KERD of the metastable dissociation.

The vacuum UV photoabsorption spectrum of methyl chloride (CH3Cl) and its perdeuterated isotopomer CD3Cl I. A Rydberg series analysis

“…Cl(1s 2 )C(1s 2 )Cl(2s 2 2p 6 )(1a 1 ) 2 (2a 1 ) 2 (1e) 4 (3a 1 ) 2 (2e) 4 : X 1 A 1 where the first atomic-like orbitals correspond to the inner-shell orbitals which are localized on the Cl and C atoms and have 1s, 2s and 2p character. The 1a 1 and 2a 1 correspond to the inner-valence molecular orbitals whereas the le, 3a 1 and 2e molecular orbitals have outer-valence character.…”

“…This state could correspond to a doubly excited configuration. The Rydberg state at 16.2-16.8 eV could also be able to play a role in resonant dissociative ionization as it is the case for the CH 3 + ion production from CH 3 F [7] and for the C 2 H 3 + fragment from C 2 H 3 Br [4]. 3 Cl in the present work and in previous reports [14] and [15] for both spin-orbit components: parts (a) and (b) converge to the 3/2 and 1/2 components of the ionic 2 …”

“…We extensively examined the vacuum UV spectroscopy, the photoelectron spectroscopy (TPES and He-I) and the mass spectrometric photoionization of the halogenated derivatives of methane and ethylene. For many cases, the major importance of the localization and identification of neutral molecular states embedded in the ionization continua has been demonstrated [3][4][5][6][7].…”

The vacuum UV photoabsorption spectroscopy of vinyl fluoride (C2H3F): The vibrational fine structure and its analysis

“…The systematic study of ethylene and of several of its halogen substituted derivatives has been initiated, e.g. for C 2 H 3 Cl [12,13], C 2 H 3 Br [14][15][16] and 1,1-C 2 H 2 F 2 [17,18], or is in progress using the same array of techniques. The vacuum UV spectroscopic data reported on vinyl fluoride are very scarce.…”

Analysis of kinetic energy release distributions by the maximum entropy method

“…In many cases [22,[37][38][39][40][41][42][43][44], the very simple expression (10) is found to provide a very good approximation to P(ε|E) if the value of the exponent k is adequately chosen. A value of k equal to 1/2 or to 1 is usually found.…”