C. Linton

Electronic states of the CeO molecule: Absorption, emission, and laser spectroscopy

Abstract The electronic spectrum of the CeO molecule is characterized by the existence of many 0-0 bands resulting from transitions between various Ω components of excited states and the 16 lower Ω states which arise from the lowest configuration… (4f)(6s). Classical studies of rotational structure of absorption and emission spectra have been extended, and argon-ion and tunable dye (coumarin 460, rhodamine 6G, rhodamine 101) lasers have been used to excite known transitions in bands which had previously been rotationally analyzed. The resulting fluorescence spectra have been used to establish the relative energies of the lower states. By tuning the lasers to excite analyzed transitions from different known electronic states it has been possible to determine the energies of 16 low-lying states, to assign quantum numbers to 14 with certainty, and to suggest assignments for the other 2. The resulting energy level diagram of lower states is discussed and shown to correlate well with the 4f6s configuration of the Ce2+ ion. From the energies of the low-lying states, those of the higher excited states are calculated and in some cases new values of vibrational and rotational constants are derived.

Ionization potentials and bond energies of TiO, ZrO, NbO and MoO

The adiabatic ionization potentials of TiO, ZrO, NbO, and MoO have been measured using two-color photoionization efficiency (PIE) spectroscopy and mass-analyzed threshold ionization (MATI). From the sharp ionization thresholds in the PIE and MATI spectra the following ionization potentials were derived: IP(TiO)=6.8197(7) eV, IP(ZrO)=6.812(2) eV, IP(NbO)=7.154(1) eV, and IP(MoO)=7.4504(5) eV. These values have been combined with the ionization potentials of the metal atoms and the bond energies of the transition metal oxide cations, D0(MO+) [M. R. Sievers et al., J. Chem. Phys. 105, 6322 (1996)] to derive the bond energies, D0(MO), of the neutral metal monoxides; D0(TiO)=6.87(7) eV, D0(ZrO)=7.94(11) eV, D0(NbO)=7.53(11) eV, D0(MO)=5.44(4) eV. It is argued that these values are more accurate than the currently accepted values and hence are recommended for future work. Experimental evidence suggests that the ground state of MoO+ is the 4Σ− state arising from the δ2σ1 configuration.

Laser spectroscopy of low‐lying excited states in YbO: Linkage of the Yb2+ f 13s and f 14 configurations

Dye laser excitation and fluorescence spectra have been used to provide information on rotational structure and energy linkages between several low‐lying electronic states of YbO. Configurational assignments of the observed low‐lying states have been made on the basis of vibrational frequencies. The X 1Σ+ ground state, with ΔG1/2=683 cm−1, is assigned to the Yb2+ 4f14 configuration, whereas five states with Ω=0−, 1, 2, 1, and 3 and ΔG1/2∼820–830 cm−1 are assigned to Yb2+ 4f136s. The lowest 4f136s(Ω=0−) state is found to be 910 cm−1 above the 4f14, X 1Σ+ state, thus establishing the linkage between the  f14 and  f13s configurations. The observed electronic states are discussed in relation to the ligand field model and the electronic state energies are fitted to determine the ligand field parameters. The configurational assignment for the YbO ground state proposed by M. Dolg and H. Stoll [Theor. Chim. Acta 75, 369 (1989)] is shown conclusively to be incorrect.

Rydberg and pulsed field ionization-zero electron kinetic energy spectra of YO

A spectroscopic study of the Rydberg states of YO accessed from particular rotational levels of the A 2Π1/2, v=0 state has been combined with a pulsed field ionization, zero electron kinetic energy (PFI-ZEKE) investigation. The results provide accurate values of the ionization energy of YO, ionization energy I.E.(YO)=49 304.316(31) cm−1 [6.112 958(4) eV], and of the rotational constant (and bond length) of the YO+ cation in its X 1Σ+, v=0 ground state, B0+=0.4078(3) cm−1 [r0=1.7463(6) A]. The improved value of I.E.(YO) combined with the known ionization energy of atomic yttrium then leads to the result D00(Y−O)−D00(Y−O)=0.1041±0.0001 eV. Combining this result with the value of D00(Y+−O) obtained from guided ion beam mass spectrometry yields an improved value of D00(Y−O)=7.14±0.18 eV. The PFI-ZEKE spectra display an interesting channel-coupling effect so that all rotational levels with J+⩽J′(A)+0.5 are observed with high intensity, where J+ is the angular momentum of the YO+ cation that is produced and J′(...

Low lying electronic states of CeO

A summary is given of the results of laser induced fluorescence experiments on the CeO molecule, which result in the determination of the relative energies of seven low lying electronic states. Both argon ion and cw dye lasers were used to excite several transitions from the X1(Ω=2), X2(Ω=3), and X3(Ω=4) states and the resulting fluorescence spectra showed that (i) the X2(3) state is 80.4±0.7 cm−1 above X1(2), (ii) X4(3) is 100.6±1.5 cm−1 above X3(4), and (iii) there are three states labeled u(2), w(3), v(2), which are 834, 2537, and 2688 (±3) cm−1 respectively above X2(3). It was also shown that the vibrational frequencies ΔG1/2, of the seven low lying states are all between 820 and 825 cm−1.

Photoluminescence of the A2Π-X2Σ+ system of the yttrium oxide molecule

Abstract A cw dye laser, tunable in the region 570–620 nm, has been used to excite photoluminescence in the A2Π-X2Σ+ system of the YO molecule. Two methods have been used to obtain spectra. They are (i) photoluminescence and (ii) spectrally selective excitation spectroscopy. The latter maintains the simplicity of photoluminescence, but has higher resolution. The spectra obtained at medium resolution (∼0.05 nm) have been surveyed and the identification of transitions has been outlined. A method was devised in which known lower state constants were used in calculating approximate upper state constants whenever the laser simultaneously excited coincident rotational transitions in the same band. From these calculations, an approximate value of α′e was calculated which was found to be close to, but slightly larger than values previously computed from the Pekeris formula. Many examples of collisional transfer were observed. In particular, maximum transfer from 2 Π 3 2 to 2 Π 1 2 was always observed to involve an increase of one unit in the vibrational quantum number. No transfer was observed between opposite parity components of Λ doublets, in spite of their closeness in energy, indicating that the symmetry of the electronic eigenfunctions was unaffected by collisions. Reanalysis of previous high resolution data has shown that, when the contribution of Λ-doubling parameters to the separation of the 2 Π 1 2 and 2 Π 3 2 states is taken into account, the value of the spin-orbit coupling constant, A, changes significantly. It was also found necessary to include the constant, AD, to account for the effect of centrifugal distortion on the spin-orbit interaction.

Fourier transform spectroscopy of the 1 3Σ+g–a 3Σ+u transition of the 6Li2 molecule

The 1 3Σ+g–a 3Σ+u transition of 6Li2 has been observed via collisionally induced fluorescence, excited by visible lines of an argon‐ion laser and detected at high resolution with a Fourier–transform spectrometer in the 8200–10 100 cm−1 region. By combining the results with previously obtained data on 7Li2 [F. Martin, R. Bacis, J. Verges, C. Linton, G. Bujin, C. H. Cheng, and E. Stad, Spectrochim. Acta Part A 44, 1369 (1988)], an accerate, isotopically consistent description of both states has been obtained for 1≤v’≤7 and 0≤v‘≤7. Equilibrium constants, Rydberg‐Klein‐Rees potential curves, and dissociation energies have been determined and found to be in good agreement with ab initio calculations. From the analysis, the following positions and dissociation energies of the two states were found. For 1 3Σ+g, Te (cm−1) is 16 328.8(1.7) and De (cm−1) is 7091.6(1.2). For a 3Σ+u, Te (cm−1) is 8183.8(1.5) and De (cm−1) is 333(1).

Laser spectroscopy of YbO: Observation and analysis of some 0+-1Σ+ transitions

Abstract Argon ion and tunable dye lasers have been used to excite different transitions in YbO. Resolved fluorescence spectra have resulted in the observation of three low lying states. Long progressions were observed in the lowest state and vibrational constants have been calculated. High resolution excitation spectra of three bands in the rhodamine 6G region have been obtained and their rotational and isotopic structure (Yb has six isotopes) analyzed. The three bands are all shown to be 0+-1Σ+ transitions where the 1Σ+ state is the lowest observed state of the molecule. Term energies and rotational constants have been determined for each state and the vibrational spacing Δ G 1 2 of the lower state has been calculated. For each state, the isotopic change in constants has been discussed and compared with theory. The isotope effect has been used to determine the vibrational numbering of the upper states and to estimate their vibrational constants. The ligand field theoretical (LFT) model for rare earth oxides is outlined and its predictions for YbO are discussed. The assignment and vibrational frequency of the lowest state are shown to be in accord with the LFT predictions. The principal constants (in cm−1) determined for 174YbO are lowest state (1Σ+): Be = 0.35236(6), αe = 0.00428(6), Δ G 1 2 = 683.107(1) ; upper state A(v = 4); T4 = 17254.584(1), B4 = 0.29296(4), ωe = 547(20); upper state B(v = 2): T2 = 16475.002(1), B2 = 0.29493(4), ωe = 585(20).

Laser spectroscopy of holmium oxide: Examination of the low-lying electronic states

Abstract Laser spectroscopic techniques have been used to examine the electronic, vibrational, rotational, and hyperfine structure of holmium oxide. Single-frequency, narrow-line (1 MHz), tunable cw dye lasers have been used to excite fluorescence in gas-phase HoO and resolved fluorescence and high-resolution excitation spectra have been obtained. Four low-lying and four higher-lying states have been observed. The energies and Ω assignments of all the states have been determined together with, in some cases, preliminary rotational constants and vibrational frequencies. The four low-lying states, including the Ω= 8.5 ground state, are shown, using ligand field theoretical arguments to result from ionically bonded Ho 2+ O 2− in which the Ho 2+ configuration is 4 f 10 ( 5 I )6 s . The energy pattern and Ω assignments are shown to be in complete accord with ligand field theory predictions. Hyperfine structure, in some cases well resolved, has been observed in all high-resolution spectra and has been used to determine the free atomic ion quantum numbers for each low-lying state. The relative magnitudes of the hyperfine splitting in each of these states are used to estimate the relative contributions of the f and s electrons to the hyperfine structure.

Laser spectroscopy of the lanthanide monofluorides: The ground state configuration of holmium fluoride

Abstract Observations of first lines in the branches of fluorescence excitation spectra of the A-X system of HoF and resolved fluorescence spectra of the B-X system have established that Ω (A) = 9 , Ω (B) = 8 , and Ω (X) = 8 . Ligand field calculations predict three low-lying Ln+ configurations, 4fN−16s2, 4fN6s, and 4fN−15d6s, for the low-lying states of the lanthanide monofluorides (LnF). The Ω = 8 assignment for the X state establishes that the ground state configuration of HoF is 4f106s2. Vibrational frequencies of ωe ∼ 600, 550, 500 cm−1, respectively, are suggested as diagnostics of the fN−1s2, fN−1sd, and fNs superconfigurational character for all low-lying states of all LnF molecules. A rotational analysis of the A-X system has been performed and the molecular parameters are presented. Hyperfine structure is not resolved but the hyperfine widths of the broadened lines (P > Q > R) indicates that the hyperfine splitting is larger in the A than in the X state.