Multi-isotopologue analyses of new vibration-rotation and pure rotation spectra of ZnH and CdH

High resolution infrared emission spectra of ZnH, ZnD, CdH, and CdD have been recorded with a Fourier transform spectrometer. The v = 1 → 0 and v = 2 → 1 bands of ZnH, ZnD, CdH, and CdD, as well as the v = 3 → 2 band of ZnD were observed for the X²Σ⁺ ground electronic state. In addition, new rotational spectra have been recorded for CdH and CdD using a tunable far-infrared spectrometer, and pure rotational transitions in the v = 1 level of the ground state were measured. The new data were combined with the previous data from diode laser infrared spectra and pure rotation spectra of ZnH/ZnD and CdH/CdD available in the literature. The data from all isotopologues were fitted together using a Dunham-type energy level expression for ²Σ⁺ states, and Born-Oppenheimer breakdown correction parameters were obtained. The equilibrium rotational constants (B_e) of ⁶⁴ZnH, ⁶⁴ZnD, ¹¹⁴CdH, and ¹¹⁴CdD were determined to be 6.691332(17), 3.402156(7), 5.447074(18), and 2.750761(6) cm⁻¹, respectively, and the associated equilibrium internuclear distances (r_e) are 1.593478(2), 1.593001(2), 1.760098(3), and 1.759695(2) Å, respectively. Simple reduced mass scaling for the spin-rotation interaction constants of ZnH and CdH fully accounted for their isotopologue dependence, and no Born-Oppenheimer breakdown correction was required for these parameters.     

The Electronic Spectrum of NiCN in the Visible Region

The electronic spectrum of NiCN in the 500-630 nm region has been observed by laser-induced fluorescence, following the reaction of laser-ablated nickel atoms with cyanogen under free jet expansion conditions. Seven electronic states have been identified. Three of these, X?₁²Δ_5/2, X?₂²Δ_3/2, and W?₁²Π_3/2, are derived from the electron configuration Ni⁺ (3d⁹) CN⁻, and the other four, òΔ_5/2, B?²Π_3/2, C?²Φ_7/2, and D?²Φ_5/2, are derived from the configuration Ni⁺ (3d⁸ 4s) CN⁻. Rotational analysis of bands of NiC¹⁴N and NiC¹⁵N at high resolution has given the bond lengths in the X?₁²Δ_5/2 ground state as r₀ (Ni-C)=1.8292±0.0028 Å; r₀ (C-N)=1.1591±0.0029 Å. The orbital angular momentum splits the bending fundamental of the X?₁²Δ_5/2 state into two vibronic components, which lie at 243.640 cm⁻¹ (²Π_3/2) and 244.964 cm⁻¹ (²Φ_7/2). Exceptionally strong Fermi resonance occurs in the ground state between the Ni-C stretching vibration, ν₃, and the overtone of the bending vibration. Sixty vibrational levels of the ground state with |l|=0 and 1 have been assigned. They could be fitted by least squares to a simple matrix representation of the Fermi resonance that ignores the orbital angular momentum; the interaction matrix element, as a fraction of the bending frequency, turns out to be larger than that in the “prototype” molecule, CO₂. The two low-lying excited electronic states, X?₂²Δ_3/2 at 830 cm⁻¹ and W?₁²Π_3/2 at 2238 cm⁻¹, have very similar properties to the ground state. The energies of the excited states in the visible region bear a remarkable resemblance to those found in NiH (S. A. Kadavathu et al., 1991, J. Mol. Spectrosc.147, 448-470). Again, the effects of Fermi resonance in them are large but those of vibronic coupling are surprisingly small. The most significant vibronic coupling occurs between the òΔ_5/2 and B?²Π_3/2 states, which are separated by 79 cm⁻¹, an interval which is less than half the frequency of the bending vibration that couples them; large numbers of vibronically induced bands appear in the excitation and dispersed emission spectra, but the splitting between the vibronic components of the bending fundamental of the òΔ_5/2 state is only 6.988 cm⁻¹. Rotational perturbations are widespread in the òΔ_5/2 state, particularly in the levels of the ν₃ (Ni-C stretching) progression. Vibrational assignments have been made on the basis of the ⁵⁸Ni-⁶⁰Ni isotope shifts at high resolution and the Franck-Condon patterns in dispersed emission spectra. Various weak unassigned bands, both in the excitation and the dispers ed emission spectra, give evidence for the existence of at least three more excited electronic states which it has not been possible to characterize in detail.     

The ultraviolet spectrum of the CoCl2 radical, studied at vibrational and rotational resolution

The laser excitation spectrum of the 327 nm band system of CoCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. The spectrum is congested and suffers extensive perturbations. A progression in the excited state symmetric stretching vibration has been identified. The decrease in the symmetric stretching vibrational wave number on excitation is considerable [nu1 '=195.7(12), nu1 (")=358.1(17) cm(-1)]. Despite widespread perturbations in the rotational structure of these vibronic bands, they can be confidently assigned to a parallel Omega=72-72 transition, consistent with an inverted 4Deltag ground electronic state. The rotational constant for Co35Cl2 in the ground state is determined to be 0.056 65(11) cm(-1), which corresponds to a value for the zero-point averaged Co-Cl bond length r0 of 2.062 8(40) A. The perturbations are found to be strongly isotopomer dependent.     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

Electronic spectrum of TaO and its hyperfine structure

The B (2)Phi(5/2)-X(1) (2)Delta(3/2)(0,0) band at 778 nm and the C (2)Delta(3/2)-X(1) (2)Delta(3/2)(0,0) band at 737 nm of tantalum oxide (TaO) were recorded by laser excitation spectroscopy using a hollow cathode sputtering source to generate the molecules. The hyperfine structure arising from the (181)Ta (I=72) nucleus was measured at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure was assigned and fitted in order to derive accurate values for the magnetic dipole and electric quadrupole interactions. The magnetic hyperfine constant for the ground electronic state was also calculated using the density functional theory as h(3/2)=625 MHz, in good agreement with the experimental value of 647+/-10 MHz. This result suggests that the X (2)Delta ground state of TaO is well described by a pure deltasigma(2) electronic configuration, where the unpaired electron is located in a Ta 5ddelta orbital.     

The isotopic dependence of the spin-rotation interaction: the rotational spectrum of cadmium hydride in its XΣ state

Far-infrared rotational transitions within the X²Σ⁺ (v=0) state of cadmium hydride (CdH) were recorded over the range N″=2-17 for 12 different isotopomers, using the technique of tunable far-infrared (TuFIR) spectroscopy. The molecule was made by heating cadmium metal in the presence of a DC electric discharge in hydrogen. Fine structure arising from the electron spin-rotation interaction and hyperfine structure from the ¹¹¹Cd, ¹¹³Cd, and ¹H nuclei were resolved and analyzed. All of the isotopic data were fitted together using a Hamiltonian containing mass-independent, Dunham-type rotational parameters U_kl and small correction terms Δ_kl described by Watson [J. Mol. Spectrosc. 80 (1980) 411]. The spin-rotation interaction was modeled in an analogous way using Dunham-like U_γ,kl parameters, and fitting its isotopic dependence properly required the use of four Δ_γ,kl correction terms.