Neon matrix ESR and CI theoretical investigation of AlF+; photoionization of AlF from thermal and laser sputtering generation methods

Abstract

The high-temperature AIF' radical cation has been generated by the photoionization of AlF(g) produced both by a laser sputtering method and high-temperature vaporization reactions. This represents the first spectroscopic study of AIF' and establishes its ground electronic state as 22. The ESR spectrum of the AIF+ radical, isolated in a neon matrix at 4 K, has been analyzed in detail, and the experimental magnetic parameters obtained show excellent agreement with the results of an extensive ab initio theoretical calculation. The AIF' magnetic parameters in a neon matrix are the following: g,, = 2.0015 (S) , g, = 2.0000 (5); AI, All = 2893 (8) MHz, A , = 2782 (6) MHz, I9F, A,, = 473 (5) MHz, A , = 90 (5) MHz. The electronic structure of AIF' is compared to the isoelectronic series 29SiO+, AIO, and MgF utilizing both experimental and theoretical findings. Orbital populations for the unpaired electron were obtained from the commonly applied free atom comparison method (FACM) and from a Mulliken type population analysis of a CI wave function which yielded magnetic parameters in close agreement with experiment. The effect of 'corwther valence overlap" was studied in detail for this isoelectronic series. This A l p study and a previous one for SiO+ are apparently the first ESR investigations of high-temperature inorganic cation radicals. Generation and trapping techniques have been developed to permit the ESR (electron spin resonance) investigation of small, highly reactive cations having relatively large electron affinities in neon matrices near 4 K. Examples of cations recently studied by ESR with these neon matrix trapping techniques include CO+,I NH3+,' N2+,2 H20+,3 H2CO+,4 Cd+,s CH4+: C202+,' and the high-temperature cation radical 2gSiO+.8 Experimental results have also been obtained for a few anion radicals trapped in neon matrices as free ions including F2-,9 H F , I 0 DF,Io CI,-,'O and HCI-.'O The Cl; and HCI-radicals have been previously studied by ESR as chemically bonded ion pairs, M'X-, in argon ma-The inert nature of the neon host, its low polarizability, and large ionization energy (21.6 eV) allow free or gas-like properties of ions to be obtained. Cations having electron affinities much greater than 10-1 1 eV apparently cannot be stabilized in other matrix materials such as argon or freon matrices. Paramagnetic ions trapped in frozen ionic solutions or crystalline hosts can be highly perturbed, and the information obtained might not accurately represent the inherent properties of the trapped species. This AIF' study illustrates that the matrix isolation trapping method could be applied to a wide range of charged and neutral chemical systems produced by reactive laser sputtering processes. The reactive intermediates produced by such laser induced gassurface reactions could be characterized by the wide range of spectroscopic methods currently used with the matrix isolation technique. Current research efforts in our laboratory are using this laser technique to produce metal nitride neutral and cation radica...

Laser vaporization generation of B 14NH, B 15NH, B 14ND, B 16O, and B 17O: Electron-spin-resonance investigation in neon matrices under ultracold trapping conditions

“…This observation is consistent with a similar detailed comparison of the two generation methods conducted for the BF + (X 2~) radical in neon matrices. 18 The significant difference between this neon matrix ESR spectrum ofBO obtained under ultracold trapping conditions and that reported earlier under the more ordinary trapping conditions is the extent of separation between the much weaker parallel (8 = 0°) line and its corresponding perpendicular (8 = 90°) component for a given hyperfine transition of liB 16 0 or lOB 16 0. 1 It is this critical separation which determines the value of the A dip parameter which is transitions of "B '00 are shown for a neon matrix sample deposited under ultracold trapping conditions.…”

The AlCO− and Al(CO)2− anions: Matrix isolation infrared spectra and density functional theory studies

“…On the other hand, cations can be produced by ion-molecule reactions or via photoionization by radiation in the ablation plume. [25][26][27] The laser-ablated metal concentrations in matrix samples are of interest. Although we cannot directly measure the amount of metal deposited in matrix, and there is some variation in different experiments, qualitative comparison with previous thermal Al atom reactions provides the basis to estimate the metal molar concentration in our laser ablation experiments.…”

Laser vaporization generation of the diatomic radicals PdB, 105PdB, PdAl, and 105PdAl: Electron spin resonance investigation in neon matrices at 4 K

“…In fitting the observed ESR line positions of PdAI and the other radicals analyzed in this report, an exact diagonalization treatment of the following spin Hamiltonian was employed using programs developed previously in our laboratory: 16,19,21 where all symbols have their standard meanings and the sum is over both magnetic nuclei. 5 It was not necessary to include quadrupole terms in order to obtain agreement between observed and calculated line positions within the experimental uncertainty of ± 1 G for all cases.…”