TY - JOUR
T1 - Quantum-resolved angular distributions of neutral products in electron-stimulated processes
T2 - NO desorption from and NO2 dissociation on Pt(111)
AU - Burns, A. R.
AU - Stechel, E. B.
AU - Jennison, D. R.
N1 - Funding Information:
The authors gratefully acknowledgec ritical commentsf rom N.D. Shinn. This work was supported by the US Departmento f Energy under Contract No. DE-AC04-76DP00789.
PY - 1993/1/10
Y1 - 1993/1/10
N2 - We present the first quantum-resolved angular distributions of ground-state neutral molecules which are products of electron stimulated desorption (ESD) and electron stimulated dissociation. Laser resonance-enhanced multiphoton ionization (REMPI) and two-dimensional imaging have been used to obtain angular distributions of NO desorbed by 350 eV electrons from O-precovered Pt(111). In a similar fashion, we have measured angular distributions for the NO product of NO2 dissociation on clean and O-precovered Pt(111). In all cases, we observe narrow widths which are roughly the same as ion distributions determined by ESDIAD (ESD ion angular distributions). The angular distribution for NO ESD is sharply peaked (7° half-width at half maximum) along the surface normal for an O coverage (θo) of 0.25 monolayer (ML). The angular distribution of the NO product from dissociation of side-bonded NO2 on clean Pt(111) is unexpectedly peaked about the surface normal, and thus does not reflect dissociative forces parallel to the surface or the ∼ 25° off-normal ground-state bond direction. On O-precovered Pt(111), where NO2 is N-bonded, ∼ 6° off-normal beams are observed. When the substrate is precovered with θo > 0.5 ML, local disorder creates asymmetric site geometries which result in multiple peaked angular distributions with both normal and off-normal (∼9-10°) components; similar effects for NO ESD are observed. In all these studies, the NO angular distributions are invariant to rotational or vibrational state. This implies that the lateral translational degrees of freedom are essentially de-coupled from the internal modes of the molecule. The results are discussed in terms of desorption mechanisms, dissociative forces, site geometries, and disordered coadsorbate layers.
AB - We present the first quantum-resolved angular distributions of ground-state neutral molecules which are products of electron stimulated desorption (ESD) and electron stimulated dissociation. Laser resonance-enhanced multiphoton ionization (REMPI) and two-dimensional imaging have been used to obtain angular distributions of NO desorbed by 350 eV electrons from O-precovered Pt(111). In a similar fashion, we have measured angular distributions for the NO product of NO2 dissociation on clean and O-precovered Pt(111). In all cases, we observe narrow widths which are roughly the same as ion distributions determined by ESDIAD (ESD ion angular distributions). The angular distribution for NO ESD is sharply peaked (7° half-width at half maximum) along the surface normal for an O coverage (θo) of 0.25 monolayer (ML). The angular distribution of the NO product from dissociation of side-bonded NO2 on clean Pt(111) is unexpectedly peaked about the surface normal, and thus does not reflect dissociative forces parallel to the surface or the ∼ 25° off-normal ground-state bond direction. On O-precovered Pt(111), where NO2 is N-bonded, ∼ 6° off-normal beams are observed. When the substrate is precovered with θo > 0.5 ML, local disorder creates asymmetric site geometries which result in multiple peaked angular distributions with both normal and off-normal (∼9-10°) components; similar effects for NO ESD are observed. In all these studies, the NO angular distributions are invariant to rotational or vibrational state. This implies that the lateral translational degrees of freedom are essentially de-coupled from the internal modes of the molecule. The results are discussed in terms of desorption mechanisms, dissociative forces, site geometries, and disordered coadsorbate layers.
UR - http://www.scopus.com/inward/record.url?scp=0027261613&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0027261613&partnerID=8YFLogxK
U2 - 10.1016/0039-6028(93)90688-G
DO - 10.1016/0039-6028(93)90688-G
M3 - Article
AN - SCOPUS:0027261613
VL - 280
SP - 359
EP - 368
JO - Surface Science
JF - Surface Science
SN - 0039-6028
IS - 3
ER -