Heteronuclear molecules from matrix isolation sublimation and atomic diffusion

Abstract

We demonstrate the production of cryogenic beams of heteronuclear molecules from the matrix isolation sublimation (MISu) technique. A sapphire mirror serves as a substrate whereupon a solid Ne matrix is grown. Atoms of Li, H, Ca, and C are implanted into the matrix via subsequent laser ablation of different solid precursors such as Ca, Li, LiH, and graphite. The matrix is sublimated into vacuum generating a cryogenic beam of Ne carrying the previously isolated neutral atomic and molecular species. A compact and low energy electron source and time-of-flight mass spectrometer was designed to fit this system at low temperature. With electron ionization time-of-flight mass spectrometry, we analyze the species coming from MISu and demonstrate the formation of heteronuclear molecules in the matrix. In this first study, we produced LiCa from the sequential implantation of Li and Ca into the matrix and some clusters of CLi after Li and C ablation. Also from ablation of a single LiH pellet, we observed clusters of LiH. This novel technique opens up the opportunity to generate cryogenic beams of different molecules for precision physics and chemistry studies. Laser or microwave high resolution spectroscopy of a molecular beam benefits from low translational and rovibrational temperatures and forward velocities, such as the ones produced in this technique. Toward the prospect of enhancing the molecular formation, we introduce a new method to study the atomic diffusion of Li and Ca in the Ne matrix via laser spectroscopy during sublimation. We estimate a small diffusion coefficient at 7 K, but a surprisingly linear atomic dispersion during sublimation. The method is extensive to other species and matrices.

Trapping and thermal migration of the first- and second-row atoms in Ar, Kr and Xe crystals

“…Studying the generation of cryogenic molecules by sublimation of the Ne films with the atomic species codeposited by ablation, Oliveira et al attributed the release of atomic species to their diffusion across the matrix. 21 Laser spectroscopy of the released Li atoms gave the value of order of 10 À16 cm 2 s À1 for the diffusion coefficient through the films less than 600 nm thick at 7 K, which corresponds to the rate k = 1 s À1 . This value seems to be too high to be attributed to the true TIM.…”

“…In the classical Ar, Kr and Xe rare gas (RG) matrices, TIM was observed for light atomic species. Direct and indirect indications of the TIM were reported for the majority of the first-and second-row atoms, namely, for H, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Li, 20,21 B, 22,23 C, [24][25][26][27][28][29] N, [30][31][32][33][34] O (see ref. 35 and references therein) and F. [36][37][38][39][40][41][42] However, the TIM activation energies and rates were reliably determined in the selected RG matrices only for H [5][6][7]9,12,13,15 and O…”