Rotational study and hyperfine effects of the (0,0) band of the B2Σ-X2Σ system of ScS

Rotational analysis of the (0,0) band of the B²Σ-X²Σ transition of ScS is reported. Spectrographic illustration of a hyperfine coupling transition in the ground state is demonstrated for the first time. This enables an order of magnitude to be obtained for γ″ (～0.003 cm^?1). The results for the other constants were: X state: B″ = 0.1971 cm^?1, D″ = 5 × 10^?8cm^?1, 4b = 0.23 cm^?1 (equal to that for ScO within the limits of measurement uncertainty); B state: B′ = 0.1853 cm^?1, D′ = 6 × 10^?8cm^?1, γ′ = ?0.0594 cm^?1, which can be compared with p_A²Π = 0.060 cm^?1. It was found that the two excited states A²Π and B²Σ constitute an excellent example of pure precession (p_pp = 0.058 cm^?1, and this enables the vibrational levels of A²Π to be numbered.     

Laser spectroscopy of the A[16.4]8.5-X7.5, A[16.4]8.5-Y[0.15]8.5, and A[16.4]8.5-Z[0.85]7.5 transitions of dysprosium monochloride

Laser-induced fluorescence spectra have been obtained at low resolution using a laser ablation source and pulsed dye laser, and at high resolution using a Broida oven and cw ring dye laser. Dispersed fluorescence spectra from two different excited states, A[16.4]8.5 and B[15.4]Ω (unknown Ω) (the states are labelled [10⁻³T₀]Ω according to their energy and Ω assignment) showed transitions to the same four low lying electronic states, X7.5, Y[0.15]8.5, Z[0.85]7.5, and an unassigned state at 970 cm⁻¹. High resolution excitation spectra of the A-X 0-0, A-Y 0-0 and 0-1, and A-Z 0-0 and 0-1 transitions were obtained and a global fit to all the data yielded rotational constants for both ¹⁶²Dy³⁵Cl and ¹⁶⁴Dy³⁵Cl. From the band origins, vibrational frequencies of 291 and 284 cm⁻¹ were obtained for the Y[0.15]8.5 and Z[0.85]7.5 states, respectively, suggesting that these two states originate from the Dy⁺(4f¹⁰6s)Cl⁻ configuration. The ¹⁶²Dy-¹⁶⁴Dy and ³⁵Cl-³⁷Cl isotope effects were studied and both indicated a ground state, X7.5, vibrational frequency of ∼230 cm⁻¹ which was reinforced by the observation, in dispersed fluorescence from the B[15.4] state, of a weak transition to a state 233 cm⁻¹ above the ground state. The observed electronic states and their configurational origin are discussed in terms of ligand field theory predictions.     

The B2Σ+ state of zinc deuteride

Conventional high-resolution photographic spectroscopy has been employed to study the B²Σ-X²Σ emission system of zinc deuteride in the region 280–370 nm. The B-X system of ZnD is reported for the first time and 17 such bands have been rotationally analyzed. Many local rotational perturbations have been found in the B state and are attributable to interactions with the A²Π state. The rotational and vibrational data for ZnH (after Stenvinkel) and ZnD are complementary and enable the RKR curve for the B state to be mapped with reasonable accuracy for almost 10 000 cm⁻¹. B-X Franck-Condon factors for ZnH and ZnD are also reported.     

Intensity perturbation in the B2Σ-X2Σ band system of SrF

The intensity anomaly of the B²Σ-X²Σ system of SrF was analyzed based on the interaction between the A²Π and B²Σ states. The theoretical relative intensity was calculated from overlap integrals and spectroscopic constants previously obtained. Comparison between theoretical and observed intensities showed that the electronic transition moment of the B-X system is the same order of magnitude as that of the A-X system.     

Born-Oppenheimer breakdown effects in the determination of diatomic internuclear potentials: Application of a least-squares fitting procedure to the HCl molecule

This paper describes a least-squares fitting procedure for the reduction of measured line positions in ¹Σ diatomic spectra to effective internuclear potentials. The procedure, which is based on first-order perturbation theory/Hellman-Feynman theorem, can be applied to data within a single electronic state, or to such data in combination with those of an electronic transition. Following recent theoretical work on Born-Oppenheimer breakdown, a modified, or effective, vibration-rotation Hamiltonian is employed to take account of non-adiabatic effects. An unlimited amount of data can be fitted simultaneously, with appropriate weighting. Results are described from an application of the procedure to the extensive data available for H³⁵Cl (X¹Σ⁺), including those from a recent study of the B → X system. Combined with similar results from vibration-rotation data for H³⁷Cl and D³⁵Cl, the effective potentials for the ground states of the three isotopes lead to a determination of the Born-Oppenheimer potential for HCl (X¹Σ⁺). The synthetic vibration-rotation spectrum of D³⁷Cl, obtained from the eigenvalues of the calculated effective Hamiltonian for this isotope, is found to be in excellent agreement with the precise experimental data from Fourier transform spectroscopy.     

Electronic structure and reactivity of the CNO/NCO/CON isomers

Three-dimensional potential energy surfaces (PESs) have been calculated for the lowest electronic states of NCO, CNO and CON isomers, using internally contracted Multi Reference Configuration Interaction (MRCI) and Coupled-Clusters RCCSD(T) ab initio methods. For the low lying doublet and quartet excited states of the three isomers, the N–CO, O–CN, C–NO and C–ON collinear dissociation paths were mapped by the Complete Active Space SCF (CASSCF) approach and the energy variations with the bending coordinate have been explored. Several regions of conical intersections have been located and the spin–orbit interactions between states of different spin symmetry have been evaluated in the region of intersections of these states. The analysis of the PESs allows one to identify the main interactions governing the reactivity of the lowest electronic states. The NCO and CNO isomers have stable X²Π electronic ground states, for CON the X²Π ground state is separated from the dissociative [CO?+?N] asymptote by a barrier of 0.11 eV and crosses the dissociative ⁴Σ ^- state close to its minimum. At their equilibrium ground state geometries the spin–orbit interactions A _SO between the two electronic components of the X²Π states were calculated to be -95.6, -109.6 and -57.1 cm^?1 for NCO, CNO and CON, respectively. The predissociation of the vibrational levels of the A²Σ⁺ and B²Π states of NCO has been explained.     

The Ground StateXΣof NaK Revisited

Laser-induced fluorescence (LIF) optical spectra of theD¹Π–X¹Σ⁺system of the NaK molecule have been reinvestigated. In this new analysis, quantum numbers have been assigned to 3000 selected fluorescence lines for a wide range of vibrational and rotational levels (J≤ 149,v′ ≤ 23,v″ ≤ 47). A new set of constants of theX¹Σ state (Dunham-type coefficients) and term values of theD¹Π state have been determined by a weighted least-squares fit of the LIF optical lines of theD–Xsystem, some lines of theC–Xsystem, and microwave spectral data reported recently. Constants forX¹Σ (in cm⁻¹) are as follows: ω_e= 123.993, ω_ex_e= 0.3045,B_e= 0.095229, and α_e= 4.48 × 10⁻⁴. The equilibrium internuclear distance isr_e= 3.49903 Å, very little changed from the microwave value.     

Selective isotope excitation of fluorescence of CuI

The resonance fluorescence spectra of CuI vapor excited by single-mode argon ion laser lines have been obtained and analyzed. Isotopic molecules of cuprous iodide, Cu⁶³I and Cu⁶⁵I, have been selectively excited. The transitions involved are found to involve the C¹Σ-X¹Σ and A¹Σ-X¹Σ systems. The rotational constant of the A-band system of Cu⁶⁵I is determined to be 0.0670 cm^?1. The other molecular constants obtained are in good agreement with previously reported data.Vibrational energy transfer is evident, but no significant rotational broadening or new rotational lines have been observed over the temperature range studied.     

Laser spectroscopy of YBr: rotational analysis of the B1Π—X1Σ system

The (ν,0) bands, for ν = 0–5, of the B¹Π-X¹Σ transition of YBr between 806.2–891.2 nm have been studied using the technique of laser vaporization/reaction with supersonic cooling and laser-induced fluorescence spectroscopy. Spectra of both the Y⁷⁹Br and Y⁸¹ Br isotopic molecules were observed and analysed. A least-squares fit of all the measured line positions yielded vibrational and rotational constants for the B¹Π state. The equilibrium bond length of the B¹Π state is determined to be 2.622 5(2) Å.     

Laser spectroscopy of the B[17.7]8-X8 and C[19.3]9-X8 transitions of holmium monochloride

Several new transitions of holmium monochloride (HoCl) have been studied at high resolution using laser excitation spectroscopy. Two main transitions, B[17.7]8-X8 and C[19.3]9-X8 have been observed and five bands, 0-0, 0-1, 1-0, 1-1, and 2-1 of the B-X transition and three bands, 0-0, 0-1, and 0-3 of the C-X transition have been obtained at high resolution and rotationally analyzed. Among several low lying states observed in dispersed fluorescence was a strong transition from the C state to a state ∼2140 cm⁻¹ above the ground state. Excitation spectra of this transition have shown that there are apparently two states, ∼6 cm⁻¹ apart. Comparison with ligand field theory calculations are consistent with assigning these states to the excited low lying Ho⁺(4f¹¹6s)Cl⁻ configuration. Several other low lying electronic states have been observed in dispersed fluorescence spectra. Although their assignments could not be established, their energies suggest that they are from the Ho⁺(4f¹⁰6s²)Cl⁻ or Ho⁺(4f¹¹6s)Cl⁻ configurations. Rotational constants have been obtained for the B[17.7]8 and C[19.3]9 states and have been used to speculate on the possible electron configurations for these states.     

Spectra and structure of organogermanes: Microwave and Raman spectra of methyltrichlorogermane

The microwave spectrum of methyltrichlorogermane has been investigated in the region 26.5 to 40.0 GHz. The ground state rotational constants, B, were found to be 1602.19, 1601.42, 1601.10, 1600.71, 1600.02, 1537.84, 1537.10, and 1536.36 MHz for the symmetric top molecules CH₃⁷⁰Ge³⁵Cl₃, CH₃⁷²Ge³⁵Cl₃, CH₃⁷³Ge³⁵Cl₃, CH₃⁷⁴Ge³⁵Cl₃, CH₃⁷⁶Ge³⁵Cl₃, CH₃⁷⁰Ge³⁷Cl₃, CH₃⁷²Ge³⁷Cl₃, and CH₃⁷⁴Ge³⁷Cl₃, respectively. For the asymmetric top molecules CH₃⁷²Ge³⁵Cl₂³⁷Cl and CH₃⁷⁴Ge³⁵Cl₂³⁷Cl the ground state rotational constants A, B, and C were found to be 1597.96, 1559.31, 1203 and 1597.17, 1558.59, 1207 MHz, respectively. From the rotational constants the r_s values for the GeCl bond distance of 2.135 ± 0.006 Å and the CGeCl bond angle of 106.0 ± 0.7° were obtained. The centrifugal distortion constant for the CH₃Ge³⁵Cl₃ species was calculated to be 0.35 ± 0.08 kHz. The Raman spectra of methyltrichlorogermane has been recorded in the gas phase and the methyl torsional overtone (Δν = 2) was observed. From the observed frequency shift the barrier to internal rotation has been calculated to be 1.45 kcal/mole.     

Lifetime of the B3Π state of ZrO

The radiative lifetime of the J′ = 77, v′ = 0 level of the B³Π state of ZrO is 32.5 ± 2 nsec, as measured by the decay of resonant fluorescent radiation of vapor in a furnace. Transition rates and oscillator strengths have been calculated for the β-system (B³Π - X¹³Δ).     

Microwave spectra of the Cl and Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin-rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C³⁵Cl³⁷Cl and C³⁷Cl₂ of dichloromethylene in the ground vibronic state were recorded in the range 10-33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl₂ was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin-rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C³⁵Cl₂ [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50-55.] a refined r₀ structure was determined. The spin-rotation interaction constants of all three isotopomers were used to derive ³⁵Cl and ³⁷Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.     

Rotational analysis of the B3Π(0+) → X1Σ+ band systems of 35Cl35Cl and 35Cl37Cl in the chlorine afterglow emission spectrum

The B³Π(0⁺) → X¹Σ⁺ band system of Cl₂, excited by the recombination of ground state $\text{Cl}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ atoms at total pressures near 2 Torr, has been rotationally analyzed in the range 6300–9900 Å. About 30 bands, with 0 ≤ v′ ≤ 6 and 5 ≤ v″ ≤ 14, were investigated, mostly for both ³⁵Cl³⁵Cl and ³⁵Cl³⁷Cl. The band origins and rotational constants for the B state were obtained with the help of the known constants for the ground state. The principal molecular constants (cm^?1) for the B³Π(0⁺) state of ³⁵Cl³⁵Cl are as follows: T_e′ = 17 817.67(3); ω_e′ = 255.38(3); ω_e′x_e′ = 4.59(1); ω_e′y_e′ = ?0.038(8); D_e′ = 3341.17(14); B_e′ = 0.16313(3); α_e′ = 2.42(3) × 10^?3; γ_e′ = ?5.7(7) × 10^?5. The equilibrium internuclear separation is 2.4311(2) Å. The results of Briggs and Norrish on a transient absorption spectrum of Cl₂ assigned as $\text{0}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{← B}{}^3\text{Π}\text{(0}{}^{\mathrm{+}}\text{)}$ are reinterpreted with the present constants.     

Franck-Condon factors and r-centroids for the B2Σ-X2Σ systems of HgCl,HgBr, and HgI

Available spectroscopic data have been analyzed and used for calculations of Franck-Condon Factors and r-centroids for B²Σ-X²Σ bands of HgCl³⁵, HgCl³⁷, HgBr⁷⁹, HgBr⁸¹, and HgI.     

Vibrational isotope shifts in the B-X system of CL2

Excitation of resolved rovibrational (υ = 5, 8, 12, 13, 24, 25 and 26) states of Cl₂ B³Π(O⁺_u) has been carried out using a narrow-band Nd-YAG pumped dye laser. Excitation spectra for several bands of the B-X system of Cl₂, showing rotationally resolved lines, have been obtained by scanning the frequency of the dye laser. Complete rotational analyses have been carried out for the two isotopic species ³⁵Cl³⁵Cl and ³⁵Cl³⁷Cl. Vibrational isotope shifts have been calculated and discrepancies with observed values, for transitions involving levels above the onset of predissociation, are discussed.     

Laser spectroscopy of the A-X transitions of CaOH and CaOD

The A-X transitions of gas phase CaOH and CaOD, produced in a low-pressure flow system, were studied by low- and high-resolution laser spectroscopy. The vibrational structure of the low-lying vibrational levels of both the A and X states were determined. A detailed rotational analysis of the (0, 0, 0)-(0, 0, 0) bands of the A-X system is presented. The spectra are well described by a²Π-²Σ model, where the molecule is linear in both states. A preliminary analysis of the (0, 1, 0)-(0, 1, 0) bands indicates that the Renner parameter ? of the A²Π electronic state is equal to 0.073(1).     

Isotope Shifts in the TiO B-X (1-0) Band

The absorption spectrum of the B³Π-X³Δ (1-0) band of the TiO molecule has been studied at sub-Doppler resolution by crossing an effusive beam of TiO with a cw tunable laser beam and by collecting the induced fluorescence light. The five bands involving the ⁴⁶Ti, ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, and ⁵⁰Ti isotopic species have been observed and interpreted. A simultaneous analysis of the five isotopic data leads to accurate molecular constants and energy levels for the B³Π electronic state.     

Time-resolved Fourier transform emission spectroscopy of AΠ-XΣ infrared transition of the CN radical

The A²Π-X²Σ⁺Δv = −3 bands of the ¹²C¹⁴N radical have been observed by time-resolved Fourier transform spectroscopy in the 1850-3100 cm⁻¹ region with a wavenumber resolution of 0.025 cm⁻¹. The radical was produced in a pulsed positive column discharge in a cyanogene and helium mixture. Seven bands of v = 0-3, 1-4, 2-5, 3-6, 4-7, 5-8, and 6-9 were analyzed to give the molecular constants of each state by least-squares fitting of 801 lines. The pulsed discharge was found to be efficient for production of CN in the excited A²Π state. The vibrational excitation temperature was determined to be 6680 ± 835 K and 6757 ± 534 K for the A²Π and X²Σ⁺ states, respectively. The population of the A²Π was found to be 4% of that of the X²Σ⁺ state in the time after turning off the discharge.