Matrix Infrared Spectra and DFT Calculations of the Reactive MH_x (x = 1, 2, and 3), (H₂)MH₂, MH₂⁺, and MH₄^- (M = Sc, Y, and La) Species

Abstract

Laser-ablated Sc, Y, and La react with molecular hydrogen to give MH, MH2 +, MH2, MH3, and MH4 - (M = Sc, Y, and La) during condensation in excess argon for characterization by matrix infrared spectroscopy. Annealing forms the dihydrogen complex (H2)MH2, which can be reduced to MH4 - by electron capture. The (HD)MHD complex exchanges hydrogen positions on broadband photolysis to form primarily the (D2)MH2 complex. Doping the samples with CCl4 to capture ablated electrons markedly increases the MH2 + infrared band intensities and decreases the MH4 - absorptions. Further annealing produces higher (H2)2MH2 complexes, which also exchange hydrogen positions. The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and MP2 theoretical calculations are employed to predict geometries and vibrational frequencies of these novel molecules, complexes, anions, and cations. Charged species from laser-ablation contribute more to the spectra of group 3 reaction products than for any other transition metal. Experiments using solid neon and pure deuterium provide complementary spectra and favor the higher (H2)2MH2 complexes.

Energy linkage between the singlet and triplet manifolds in LaH, and observation of new low-energy states

“…Comparison of spectroscopic constants determined in the present work with theory.Das and Balasubramanian 2 and later ω e = 1429 cm −1 , ω e x e = 20.93 cm −1 by Koseki et al8 for the ground state compare well with the experimental value of ω e = 1418 and ω e x e = 15.6 cm −1 .Wang et al11 have attributed a band at 1344.1 cm −1 to the fundamental vibration of LaH in argon matrix. The red shift of 74 cm −1 in Ar matrix can be understood in terms of the ionic nature of the LaH molecule.…”

Theoretical calculation of the low-lying electronic states of the LaH molecule

“…By examining Table S1, one can find that the first excited state is 3 ⌬ by adopting the small number of valence electrons, 2 and 6, but for the higher valence electrons, 8 and 10, we find that the ground state is 3 ⌸. Since the first excited state of Mukund et al 25 is the a 3 ⌬, our calculated value of T e for this state is higher than those of Mukund et al 25 and Das and Balasubramanian 5 but it is in excellent agreement with that given by Wang et al 21 based on the MP2/6-311++G(d,p)/SDD calculation. For the electronic state (1) 1 ⌸, our calculated value of T e is in good agreement with that given in Mukund et al 25 with a relative difference of 3.9% but it is lower than that of Das and Balasubramanian 5 by 1515 cm −1 , while our calculated value of T e for (1) 1 ⌬ is higher than that of Mukund et al 25 by about 2000 cm −1 .…”

“…The number of valence electrons used in the calculation has an influence on the calculated values of T e for the different electronic states. One can consider that this influence is responsible for the discrepancy between our calculated values of T e and those of Das and Balasubramanian 5 for some electronic states, while the comparison with other theoretical calculation 21 shows excellent agreement. Taking advantage of the electronic structure of the investigated electronic states of the LaH molecule and by using the canonical functions approach, the vibrational eigenvalues E v , the rotational constants B v , and the abscissas of the turning points R min and R max were calculated for the 22 lowlying electronic states.…”

Binding Motifs for Lanthanide Hydrides: A Combined Experimental and Theoretical Study of the MHx(H2)y Species (M = La−Gd; x = 1−4; y = 0−6)

“…Similar isotopic rearrangements between classical and nonclassical hydride positions have been observed in other such complexes. 6,8 Clearly, a weak dihydrogen complex is formed with GdH 2 in solid hydrogen, but our calculations find that the binding of H 2 to GdH 2 is very weak, and we cannot determine the number of such H 2 ligands. We do, however, associate the 3385 cm -1 band and the much stronger deuterium counterpart at 2441 cm -1 (H/D ratio 1.3867) with the strongest of such H-H stretching modes of this GdH 2 (HH) x complex.…”

“…Assignment to the antisymmetric stretching mode in LaH 4 -was substantiated by HD and D 2 substitution and an even stronger band at 1227 cm -1 for the corresponding YH 4 -anion. 6,24 An absorption for LaH 4 -was observed at 1102 cm -1 in solid neon, which is listed for La in Table 7. Weak bands were observed for the early Ln metal reactions in solid hydrogen in the 970-1100 cm -1 region, which also exhibited slight increases upon photolysis and early annealing ( Table 7, labeled 4 -in Figure 4).…”