Temperature dependent stereodynamics in surface scattering measured through subtle changes in the molecular wave function

Abstract

A magnetically manipulated molecular beam technique is used to change the rotational orientation of H2 molecules which collide with a stepped Cu(511) surface and explore how the polarisation dependence of...

Characterisation of magnetic atomic and molecular beamlines for the extraction of empirical scattering-matrices

“…Phys., 2024, 26, 19630-19645 | 19633 It follows that the only unknown in the signal expression given by eqn ( 5) is the scattering-matrix, which can be extracted from the experimental data as shown previously. 28,29 These empirical scattering-matrices are directly comparable to those obtained from state-of-the-art theoretical models 42 which is why the MMI experiments provide such valuable benchmarks for these calculations; both the amplitudes and phases of the S-matrix elements can be obtained, whereas other measurements, for example which measure scattering or reaction probabilities, [43][44][45] determine quantities which are equal to the square modulus of S-matrix elements. Whilst these do still have great value and play an important role in testing theoretical models, 4,6,46,47 they are insensitive to the phases of the S-matrix elements and are often also summed over more than one element of the S-matrix.…”

“…1. The experimental setup has been described previously, [28][29][30][31][32][33][34] and so only the main details will be presented here with a particular focus on how the different components are simulated which allows signals to be calculated and the S-matrix to be extracted from the data. Here, elastic scattering of H 2 in the I = 1, J = 1 state is considered, which in the presence of a magnetic field can be split into three nuclear spin projection states (m I ) which each split into three rotational orientation projection states (m J ), giving a total of nine m I , m J states, the energies of which can be calculated using the Hamiltonian defined by Ramsey.…”

“…To conclude this section, a comparison of the results obtained by fitting data using the method described above in which the transmission probabilities of the molecules through the second hexapole depends on their m I , m J state in the first hexapole (which will be described in the following as the new model), and the method of having independent hexapole probabilities characterising the transmission probabilities through the first and second arm of the machine used in previous studies 28,32 (referred to as the old model) is presented. Recently published data taken for the specular scattering of H 2 from Cu(511) at different surface temperatures 29 will be used as an example, where the analysis in that work was performed using the new model. Fig.…”

“…In ref. 29 it was concluded that the rotational selectivity and rotational polarisation (see eqn (7) and ( 8) in ref. 29 for the definition of these quantities) decreased as the surface temperature increased.…”

“…29 it was concluded that the rotational selectivity and rotational polarisation (see eqn (7) and ( 8) in ref. 29 for the definition of these quantities) decreased as the surface temperature increased. Table 2 presents the values of these parameters at the two surface temperatures obtained from the fits to the measured data using the two different hexapole probability models.…”