3488
WILLIAMWELTNER,JR.,AND DONALD MCLEOD,JR.
Spectroscopy of Titanium, Zirconium, and Hafnium Oxides in Neon and Argon Matrices at 4 and 20°K.
by William Weltner, Jr., and Donald McLeod, Jr. Union Carbide Research Institute, Tarrytown, New York
10692
(Received April 27, 1966)
T i 0 (and perhaps TiOz), ZrO, and HfO, prepared by vaporization of the solid oxides at -2500"K., have been trapped in neon and argon matrices at 4 and 20°K. The 180-substituted molecules were also prepared by passing 1802 over the corresponding heated metal. The electronic spectra of these molecules indicate that ZrO and probably HfO have a l2+ ground state as opposed to the known 3Ar ground state of TiO. For TiO, the a and y triplet-triplet gas transitions are observed, as expected. Only one other transition appears, at 6124 corresponding to Coheur's y' system or to one of Rosen's tentatively assigned systems. The triplet systems of ZrO are not observed, but the singlet A bands in the gas, assigned here as l2+ X12+, appear strongly in the matrices. The spectrum of HfO is discussed in relation to that of ZrO, and the energy levels of the three oxides assigned to configurations of a simple molecular orbital scheme. The infrared spectra of TiO, ZrO, and HfO in neon matrices yield ground state frequencies of 1005, 975, and 974 cm.-l, respectively; the gas values are 999.2, 969.7, and 967.6 (?) cm.-l.
K.,
Introduction T i 0 and ZrO are observed strongly in the spectra of classes M and S stars. Because of this, these molecules have been studied rather thoroughly, and it has been found that T i 0 has a triplet ground state, most probably 3Ar.1 I n this case Phillips showed by intensity measurements of T i 0 bands a t several temperatures in a King furnace that the lA level was -580 cm.-l higher.2 The ground state of ZrO has not been definitely established, but it is generally assumed also to be 3Ar since this is the lower state of several prominent emission systems. HfO spectra have been measured, but very little analysis has been carried out. Our recent work on TaO in solid neon at 4°K. has helped to establish a 2Ar ground state for that molecule.3 One can reason from the molecular configuration leading to such a state that the removal of one electron should yield a lB+ ground state for HfO. Since the ground state of NbO is 2A (and we assume it is also regular) one would also predict a l2+ ground state for ZrO, contrary to the current view. Hence a comparison of the absorption spectra of TiO, ZrO, and HfO at 4'K. is of value since it could be expected to resolve the discrepancy and give us more faith in our The Journal of Physical Chemistry
understanding of the electronic structure of these transition metal molecule^.^ Our purpose here has been to compare the matrix spectra of these three molecules with each other and with gas emission spectra, where known. The results of this comparison are that ZrO has a singlet ground state, and HfO probably does also. The spectra obtained further confirm the belief that neon matrix observations correlate well with gas data.
Experimental Section The apparatus and procedure are described in previous publications.6 The induction-heated furnace was used throughout this work with the sample contained in thick-walled tungsten Knudsen cells (0.16-cm. eff u~
Uhler, Dissertation, University of Stockholm, Sweden, 1954. (2) J. G. Phillips, Astrophys. J.,115, 567 (1952). (3) W. Weltner, Jr., and D. McLeod, Jr., J . Chem. Phys., 42, 882 (1) U.
(1965). (4) A preliminary
note concerning this research was recently published: W. Weltner, Jr., and D. McLeod, Jr., Nature, 206, 87 (1965). ( 5 ) W. Weltner, Jr., and J. R. W. Warn, J . Chem. Phys., 37, 292 (1962); W. Weltner, Jr., P. N. Walsh, and C. L. Angell, ibid., 40, 1299 (1964); W. Weltner, Jr., and D. McLeod, Jr., ibid., 40, 1305 (1964).
SPECTROSCOPY OF TiO, ZrO, AND HfO IN Ne AND Ar MATRICES
sion hole). Solid Til602 (Fisher reagent grade), Zi-1602 (Fisher reagent grade), and Hfl6O2 (Wah Chang Corp.; Zr, 260 p.p.m.; other elements
