Survival Probability ofH2(v=1,J=1)

Abstract

We have measured the survival probability of H2 in a single rovibrational state (v = 1, 1 = 1) scattering from a Cu(110) surface at 78 meV translational energy, using molecular beam and laser state preparation techniques.The integrated survival probability is found to be only 0.74~0.13, compared with 1.00 for the (v = O, J = 1) state. Possible loss channels for the vibrationally excited H2, including dissociation and inelastic scattering, are discussed. PACS numbers: 82.65.Pa, 34.50.Lf, 34.50.Pi, 68.35.Ja The hydrogen/copper system has become a prototype for studying activated dissociative adsorption for both experiment and theory [1,2]. On the experimental side, molecular beam studies of adsorption [3 -6] and laserbased studies of desorption [7,8] have gone a long way towards characterizing general trends in the translational, rotational, and vibrational state dependence of adsorption and desorption. On the theoretical side, advances have been equally impressive, with multidimensional first-principles potential energy surfaces being published [9 -12] and dynamical calculations on these surfaces verifying qualitatively the experimental trends. The dissociative adsorption of H2 on copper is thought to be dominated by vibrationally excited molecules at low ((0.4 eV) incident translational energy [1,2,4]. To explore this possibility, scattering experiments in which the translational and vibrational degrees of freedom of the molecule are controlled independently are needed. These results provide an important test of models for activated sticking and mode-specific surface dynamics.Several groups have used seeded molecular beams generated with heated nozzles to gain partially independent control over the translational and internal (rovibrational) excitation of the incident molecules [4,6]. Their studies demonstrated that internal excitation can be effective in overcoming the barrier to dissociative adsorption. In these studies, however, the incident molecules have thermal distributions of rovibrational states; this complicates interpretation of the results for individual states. Hodgson, Moryl, and Zhao [5] performed a heated nozzle experiment using laser-ionization detection to measure the survival probability of a selected rovibrational state.Again, however, a thermal distribution is present in their incident beam. In addition, they scale their measured reAectivity to the scattered ground state intensity to avoid integrating over the scattering angle.Here we present the first results of our scattering experiment using both laser state preparation and detection to gain true quantum state specificity. We report a measurement of the survival probability of H2 (v = 1, 1 = 1) scattered from Cu (110) at low incident translational energy (78 meV). Our measurement is absolute in that we have integrated the incident and scattered signal over 16 cm Cho Pulsed Nozzle Skl pie Probe Laser Beam mp Laser am ector Assembly FIG. 1. Schematic diagram of the experiment. A pulsed supersonic beam of Hq is incident normally on a Cu(11...

Diffractive and reactive scattering of (v=0, j=0) HD from Pt(111): Six-dimensional quantum dynamics compared with experiment

“…Since the early 1980s, the reactive, the rotationally elastic and inelastic, and the diffractive scattering of molecular hydrogen from metal surfaces have been studied extensively, both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretically. [17][18][19][20][21][22][23][24][25][26][27][28] Much attention has been devoted to HD scattering from Pt͑111͒ because of, inter alia, the high probabilities for rotational excitation to only a limited number of accessible rotational states.…”

Vibrational de-excitation of v=1 H2 during collisions with a Cu(100) surface

“…30 Perhaps, the experimental configuration used in the associative desorption experiments can be modified to include an H 2 molecular beam, with the use of stimulated Raman pumping to overpopulate (vϭ1, jϭ0) in the incident molecular beam. [17][18][19] The stimulated Raman pumping technique has already been used in state-to-state molecular beam experiments measuring rovibrationally inelastic scattering from (vϭ1, jϭ1) to (vЈϭ0, jЈ) states of H 2 on Pd͑111͒ ͑Ref. 19͒ and on Cu͑100͒ ͑Ref.…”

“…Changes in the azimuthal quantum number are possible for collisions at the bridge site so the fraction of the population in higher m j states is larger which increases the value of the alignment. Although it is now possible to experimentally determine the relative probabilities for vibrational de-excitation by measuring the populations of scattered molecules in particular final j states, 17 no measurements of the alignment of the scattered molecules have yet been reported. Such results would be of considerable interest, particularly if significant differences are seen in the alignments for jЈϭ j 0 and jЈу j 0 as is predicted by these calculations.…”

“…The rotational-state distribution and orientational an-isotropy of scattered molecules are explained in terms of features of the potential energy surface. Recent experimental advances, including the ability to overpopulate specific rovibrational states in molecular beams and to perform final-state population analysis, [17][18][19] offer the possibility for detailed state-to-state comparisons between the presented theoretical predictions and experimental observations yet to be performed. Some of the results we will present for the scattering of ͑vϭ1, jϭ1) H 2 can be compared to existing experimental results.…”

State-to-state scattering of metastable CO molecules from a LiF (100) surface

“…Measuring the velocity distribution, angular distribution, and internal state distribution of the scattered molecules for known parameters of the incoming beam and for a known scattering geometry, yields detailed information on the molecule-surface interaction potential. [3][4][5][6][7] A few groups have reported on scattering experiments in which vibrationally excited molecules are used [8][9][10][11] . So far, little is known about the interaction of electronically excited molecules with surfaces; the study of electronically excited molecules colliding with surfaces is thus far limited to molecules residing in the different ⍀ components of the electronic ground state.…”