Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

Abstract

, 643 (1994). The dry etching reaction of solid copper surfaces with fluorine atoms or molecules has been studied with laser-induced fluorescence spectroscopy. The reaction product, copper monofluoride, CuF, is produced in the X'C+ electronic ground state and desorbs into the gas phase at surface temperatures above approximately 750 K. Rotationally resolved LIF excitation spectra of the C ' n + XIC+ band system of CuF molecules desorbing from an isotopically purified 6 ' C~ polycrystalline sample are obtained under conditions of coherent saturation. From the product state analysis it is deduced that the rovibrational product populations are in thermal equilibrium with the surface. The same holds for the translational velocity distribution obtained by Doppler-shift measurements. A pronounced polarization effect, particularly strong for Q branch transitions, can be traced back to photoselection of single-parity levels in the A doublets of the C l n state. A theoretical analysis for the distribution of J vectors, based on the formalism of Greene and Zare, shows that the measured degree of polarization is quantitatively in agreement with an isotropic distribution of rotational angular momentum vectors. The vibrational and translational product equilibration is not affected by changing the reactants from F2 molecules to F atoms, which increases the exoergicity of the overall reaction. The results are interpreted in terms of the absence of a barrier for desorption and a long residence time of the chemisorbed CuF molecules at the copper surface. The lack of any translational and rotational cooling is discussed within the framework of a model. Faisant appel i la spectroscopie de fluorescence induite au laser, on a CtudiC la rCaction de gravure B sec de surface solides de cuivre par des atomes ou des molCcules de fluor. Le monofluomre de cuivre, CuF, produit par la reaction se forme dans 1'Ctat Clectronique fondamental X'C+ et il se dCsorbe vers la phase gazeuse B des temperatures de surface suptrieures B environ 750 K. Les spectres d'excitation LIF, rCsolus en fonction de la rotation, du systkme de bandes C ' n + X'C+ des molCcules de CuF qui se dCsorbent d'un Cchantillon polycristallin de 6 3 C~ isotopiquement purifiC, ont Ct C obtenus dans des conditions de saturation cohtrente. En se basant sur une analyse de 1'Ctat du produit, on en dCduit que les populations de produit rovibrationnel sont en Cquilibre thermique avec la surface. I1 en est de m&me pour la distribution de la vitesse de translation obtenue par des mesures de diplacement Doppler. On peut attribuer un effet important de polarisation, particulikrement fort pour les transitions des branches Q, B une photosClection des niveaux de paritC unique dans les doublets A de 1'Ctat C l n .Une analyse thCorique de la distribution des niveaux J , basCe sur le formalisme de Greene et Zare, montre que le degrC de polarisation mesurC est en bon accord quantitatif avec une distribution isotrope des vecteurs des moments de rotation angulaire. L'Cquilibre vibrationnel et tr...

State-Selective Angular and Velocity Distributions of Associatively Desorbing CuF Molecules Determined by CCD Imaging

“…The analysis of the experimental data show that the CuF molecules desorb from the surface with a cos n θ, n = 1 distribution, with a translational temperature that agrees with the surface temperature within the error limits, independent of the rovibrational levels. This, in addition to previous internal product distribution analysis, is a further proof of an indirect reaction mechanism. Hence, the steps of the F 2 /Cu system may be addressed to as …”

“…The method is applied to the F 2 /Cu gas−surface reaction. This system has been investigated thoroughly in terms of internal product-state distributions in our laboratory . The angular and velocity distributions in this study completes the product-state analysis of CuF molecules desorbing associatively from Cu surfaces.…”

Two‐Dimensional Imaging of Reactively Desorbing CuF: State‐Selective Angular and Velocity Distributions

“…The copper sample is mounted in a chamber, which is evacuated The square root refers to coherent saturation which has been determined for the conditions of this experiment (see Ref. [11]). Fluorescence detection with the CCD camera implies an integration of the intensity Ifluores.…”

“…The high sample temperature during the experiments and the fluorine exposure effectively prevent any accumulation of residual gas on the surface, as verified by Auger electron spectroscopy (AES) [12]. Artifacts due to minor surface contaminants outside the detection limit of AES can be excluded, since no time dependence of the product CuF fluorescence intensity was noticed [11]. To define the reaction region and to reduce thermal background radiation of the sample heater, the surface is covered with a tantalum aperture with an opening of 2 x 5 mm.…”

“…[6,7], is applied to the associative desorption of CuF molecules from a copper surface. For this process the internal product-state distributions including the angular momentum distribution have been obtained recently [11]. With the addition of the angular velocity distributions, presented in this contribution, the fluorine/copper system is now completely characterized in a single optical experiment.…”