Detection of neutral and ionic reaction mechanisms in molecular clusters

Abstract

Techniques based on picosecond resonance-enhanced multiphoton ionization and mass-selective ion photodissociation are described as a means for studying complex reaction mechanisms in molecular clusters. A set of experiments is described that can identify the cluster-size specific reactions that occur by the overlapping processes of neutral dissociation/fragment ionization, parent ionization/dissociation, and parent ion photoexcitation/dissociation. These molecular beam techniques are demonstrated for the case of neutral and ionic photon transfer and evaporation in clusters of phenol in (NH(3))(n), as well for radical chemistry and van der Waals dissociation in (CH(3)I) (n) clusters.

Nonadiabatic molecular dynamics simulations of the photofragmentation and geminate recombination dynamics in size-selected I2−⋅Arn cluster ions

“…In recent years, several groups have applied ultrafast spectroscopic techniques to investigate cluster fragmentation, 7-10 the competition between fragmentation and ionization, 11,12 and photoinitiated chemical reactions in clusters. 7,11,[13][14][15][16][17][18][19] The more recent experiments involve the use of both photofragmentation 20,21 and ultrafast pump-probe techniques 22,23 and have been applied to investigate the X 2 Ϫ (XϭI,Br) photodissociation and cage recombination dynamics in size selected X 2 Ϫ •S n (SϭAr,CO 2 ) ionic molecular clusters.…”

“…7,11,[13][14][15][16][17][18][19] The more recent experiments involve the use of both photofragmentation 20,21 and ultrafast pump-probe techniques 22,23 and have been applied to investigate the X 2 Ϫ (XϭI,Br) photodissociation and cage recombination dynamics in size selected X 2 Ϫ •S n (SϭAr,CO 2 ) ionic molecular clusters. 20,24,25 I 2 Ϫ exhibits a strong absorption spectrum corresponding to an electronic excitation from the bound X, 2 ⌺ u,1/2 ϩ ground state to the repulsive AЈ, 2 ⌸ g,1/2 excited state 26 ͑see Fig.…”

Effects of Matrix Structure/Acidity on Ion Formation in Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

“…That is, proton transfer must be an available nonradiative decay channel of the photoexcited matrix molecule. Steadman and Syage and Robinson and co-workers have demonstrated the influence of excitation wavelength in determining the photoionization versus ESPT reaction chemistry of aromatic acids, such as phenol, 1-naphthol, and 2-naphthol, in clusters of ammonia and mixtures of ammonia and methanol.…”

Ultrafast dynamics in isolated molecules and molecular clusters

“…(CH 3 I) n complexes have been studied by different groups (see, e.g. Zhong et al (1996), Steadman et al (1990), Poth et al (1998)). For these clusters, the excitation to the electronic A state (near 270 nm) leads to an ultrafast bond breakage of CH 3 I to CH 3 +I within about 100 fs.…”