Photodissociation Dynamics of tert-Butyl Nitrite on Ag(111):  Characterization of Translationally and Internally Excited NO Fragments

Abstract

The translational, vibrational, and rotational characteristics of nitric oxide, NO, ejected by 351 nm photodissociation of tert-butyl nitrite, (CH3)3CONO, adsorbed on Ag(111) have been investigated using resonance-enhanced multiphoton ionization time-of-flight (REMPI-TOF) and interpreted using a direct excitation and collisional relaxation model. There are three translational energy components denoted as collisionless, intermediate, and thermalized. The collisionless component has characteristics matching those found for gas phase monomer photolysis. The thermalized component has characteristics expected for NO accommodated to the substrate temperature, while the more complex intermediate component is qualitatively describable in terms of collisions of nascent energetic NO with surrounding species as it exits into the gas phase. There are strong ν‘ ‘ = 1 and 2 but negligible ν‘ ‘ = 0 contributions to the collisionless component. The collisionless component is also characterized by high rotational excitation; Gaussian rotational distributions with J max = 24.5 ± 1 for ν‘ ‘ = 1 and 29.5 ± 1 for ν‘ ‘ = 2 provide reasonable fits. The translationally thermalized component is dominated by the ν‘ ‘ = 0 vibrational state and by a Boltzmann rotational distribution (T rot = 124 ± 30 K); i.e., all three modes of motion are thermalized. The vibrational and rotational characteristics of the intermediate translational component are more complex and will require simulation and angle-resolved REMPI for fuller elucidation.

Desorption dynamics of neutral molecules in matrix-assisted laser desorption/ionization

“…In contrast, the two slow components may be due to the thermal desorption of inner crystal layers with various depths. Similar multiple velocity components have been reported in the desorption of various molecules from metal surfaces [35,37,50]. In the present study, the contribution of the two fast components increases with increase of the M/A value.…”

“…This thermalized transition process is similar to the supersonic jet expansion described by Anderson et al using the Maxwell-Boltzmann equation [48]. Similar curve fitting algorithms have also been used to interpret the molecule ejection in laser ablation [37,38]. The similar algorithm was used to determine qualitatively the most-probable timeof-arrivals in Figure 4 Notably, the increase in velocity with molar ratio implies that the transformation of photon energy to thermal energy is greatly enhanced due to the increase of THAP.…”

“…Zhiglei et al [36] Zhao et al [37] and Arnolds et al [38] presented modified Maxwell-Boltzmann functions to account for the expansion property of various systems in the literature. On the other hand, Zhiglei and coworkers combined molecular dynamics (MD) simulation with direct simulation Monte Carlo (DSMC) method to study the mechanism of MALDI using a 'breathing sphere' model [39].…”

Cold-Surface Photochemistry of Primary and Tertiary Alkyl Nitrites

“…Cyclic alkyl nitrites and longer chain primary alkyl nitrites have also been examined. These studies have involved vapor-phase experiments − as well as condensed-phase and low-temperature matrix studies. − The surface photochemistry of adsorbed tert -butyl nitrite, − isobutyl nitrite, , and methyl nitrite has been examined as well. In general, the absorption spectra for these compounds present two main transitions, a strong ππ* transition in the 220–300 nm region and a weaker nπ* band in the 300–400 nm region, the latter of which demonstrates a vibrational progression due to excitation of the NO stretching mode.…”

Quantum chemical molecular dynamical investigation of alkyl nitrite photo-dissociated on copper surfaces

“…The simulation results of this work seem reasonable since the photolysis production of pure C(CH 3 ) 3 O has already proved experimentally for TBN dissociated on the surfaces of many metal like Pt, Ag, Cu, etc. [24][25][26]38].…”