The ground state energy levels and molecular structure of jet-cooled HGeCl and DGeCl from single vibronic level emission spectroscopy

Single vibronic level dispersed fluorescence spectra of jet-cooled HGeCl and DGeCl have been recorded by laser excitation of selected bands of the A 1A"-X 1A' electronic transition. Twenty-six ground state vibrational levels of HGeCl and 42 of DGeCl were measured, assigned, and fitted to standard anharmonicity expressions, which allowed all the harmonic frequencies to be determined for both isotopomers. A normal coordinate least squares analysis obtained by fitting the harmonic frequencies yielded reliable values for five of the six force constants. The ground state effective rotational constants and force field data were combined to calculate average (rz) and approximate equilibrium (re z) structures, with re z(GeH)=1.586(1) A, re z(GeCl)=2.171(2) A, and the bond angle fixed at our CCSD(T)/aug-cc-pVTZ ab initio value of 93.9 degrees . Comparisons show that the derived bond lengths are consistent with those of the appropriate diatomic molecules in their ground electronic states and the bond angle is similar to that of germylene (GeH2). A Franck-Condon simulation of the vibrational intensities in the 0(0) (0) band emission spectrum of HGeCl using ab initio force field data shows good agreement with experiment, lending credence to the vibrational analysis of the observed spectra.     

On the statistical behaviour of molecular vibronic energy levels

Electronic spectra of polyatomic molecules often exhibit a high density of complicated energy levels, making a detailed analysis of the individual levels unfavourable. In these cases, statistical tests provide an appropriate means for analysing the spectra. Fluctuation measures are presented and evaluated for calculated and experimental molecular spectra as examples. The results are compared with the predictions of random matrix theory.     

SCF-CI studies on the electronic ground state of water: Potential energy hypersurface and spectroscopic constants

Large-scale Hartree-Fock self-consistent field calculations, employing extended Gaussian basis sets, and configuration interaction studies are performed to calculate the energy hypersurface of the electronic ground state of the water molecule and to investigate the accuracy requirements in view of the determination of molecular spectroscopic constants. From the calculated points on the hypersurface the theoretical equilibrium geometry, the force field through fourth order, the spectroscopic constants _i, x_ij, _i as well as the Darling-Dennison and Fermi resonance constants are evaluated. The CI surface yields an equilibrium structure for H₂O withr _e = 0.9501 Å and _e=105.33 ° (r _exp = 0.9572 Å and _exp = 104.52 °). The vibrational levels are obtained with a systematic error of about 2 percent and the rotational constants to about 1 percent compared to spectroscopic data. The relative energy maximum corresponding to the linear structure with = is calculated to be 11890cm^–1, within the error limits of the values deduced from experimental measurements.     

On the vibronic level structure in the NO3 radical. I. The ground electronic state

The model Hamiltonian approach of Koppel et al. [Adv. Chem. Phys. 57, 59 (1984)] is used to analyze the electronic spectroscopy of the nitrate radical (NO3). Simulations of negative ion photodetachment of NO3-, the X 2A2'<--B 2E' dispersed fluorescence spectrum of NO3, and the B 2E'<--X 2A2' absorption spectrum are all in qualitative agreement with experiment, indicating that the model Hamiltonian contains most or all of the essential physics that govern the strongly coupled X 2A2' and B 2E' electronic states of the radical. All 14 bands seen in the dispersed fluorescence spectrum below 2600 cm-1 are assigned based on the simulations, filling in a few gaps left by previous work, and 7 additional bands below 4000 cm-1 are tentatively assigned. The assignment is predicated on the assumption that the nu3 level of NO3 is near 1000 cm-1 rather than 1492 cm-1 as is presently believed. Support for this reassignment (which associates the 1492 cm-1 band with the nu1+nu4 level) comes from both the model Hamiltonian spectrum and a Fourier-transform infrared feature at 2585 cm-1 that is consistent with the large and positive cross anharmonicity between nu1 and nu4 needed for the alternative 1492 cm-1 assignment. An apparent systematic deficiency exists in the treatment of the model Hamiltonian for levels involving nu4. A discussion of the correlation between energy levels in the rigid D3h and C2v limits is illustrative, and provides insight into just how hard it is to treat the degenerate bending coordinate (q4) of NO3 accurately.     

The potential energy function for the ground state of CCl calculated from spectroscopic data

The dissociation energy (D_e= 57754±872 cm⁻¹ has been estimated for the ground state of CCl⁺ by fitting a Hulburt-Hirschfelder potential to the RKR turning points. This value of D_e has been used together with molecular constants B_e, ω_e, a_i (i= 1–6) and R_e obtained by Gruebele and co-workers to construct a potential energy function for CCl⁺ in the form of a perturbed Morse oscillator.     

Potential energy curves and calculations of spectroscopic constants for the ground state of AlC and AlN

The density functional theory method with B3LYP/6-311++G(df,pd), B3LYP/6-311++G(2df, 2pd), and B3LYP/6-311++G(3df,3pd) basis sets is used to compute the geometrics and single point energy of aluminum carbide (AlC) and aluminium nitride (AlN) in their ground state. The Level 8.0 program is used to calculate spectroscopic constants and fit the energy potential curves. The effect of a basis set on the spectroscopic constants is discussed. The results show that the calculated potential curve matches well with the Level 8.0 fitting curve, and the calculated values of spectroscopic constants become more reliable with the improvement of the quality of basis sets. The spectroscopic constants are in good agreement with the existing experimental and theoretical values. For the first time, the reliable anharmonicity constant data of AlC are reported, which agrees so well with the experimental value.     

Error bounds for the nonrelativistic electronic ground state energy of molecular hydrogen

Upper and lower bounds are calculated for the nonrelativistic electronic ground state energy of the¹ _g ⁺ state of molecular hydrogen using the method of variance minimization with Hylleraas-CI functions. In order to solve the occurring new integrals centered interparticle coordinates were introduced.     

Single vibronic level resonant Raman scattering of molecular ions in solid glass: PMDA anion and naphthalene cation

Resonant Raman spectra were obtained for the radical anion of pyromellitic dianhydride (PMDA) in MTHF glass and the radical cation of naphthalene in alkyl halide glass at 77 K by using a pulsed tunable dye laser. The intensity pattern of the single vibronic level resonant Raman resembles that of hot fluorescence when the homogeneous line width of the intermediate level is narrow. Overtones and combinations of the excited vibrational mode prevail in the spectra.     

Franck-Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity

Potential energy functions (PEFs) of the X (1)A(') and A (1)A(") states of HSiF have been computed using the coupled-cluster single-double plus perturbative triple excitations and complete-active-space self-consistent-field multireference internally contracted configuration interaction methods, respectively, employing augmented correlation-consistent polarized-valence quadruple-zeta basis sets. For both electronic states of HSiF and DSiF, anharmonic vibrational wavefunctions and energies of all three modes have been calculated variationally with the ab initio PEFs and using Watson's Hamiltonian for nonlinear molecules. Franck-Condon factors between the two electronic states, allowing for Duschinsky rotation, were computed using the calculated anharmonic vibrational wavefunctions. These Franck-Condon factors were used to simulate the single vibronic level (SVL) emission spectra recently reported by Hostutler et al. in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the A (1)A(")(1,0,0)-->X (1)A(') SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the A (1)A(")(0,1,0) and (1,1,0) SVL emissions of HSiF have been found. These are most likely, partly due to experimental deficiencies and, partly to inadequacies in the ab initio levels of theory employed in the calculation of the PEFs. Based on the computed Franck-Condon factors, minor revisions of previous vibrational assignments are suggested. The calculated anharmonic wave functions of higher vibrational levels of the X (1)A(') state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching.     

Radiative and non-radiative decay of selected vibronic levels of the state of alkoxy radicals

We have measured the lifetimes of some of the prominent bands observed in the moderate-resolution, jet-cooled laser induced fluorescence excitation spectra of the transition of ethoxy, all the structural isomers of propoxy and butoxy, and 1-pentoxy. Recent high-resolution, rotationally resolved studies on primary alkoxy radicals have given conformer specific assignments for the bands for which lifetimes have been measured. We report observed lifetime trends as a function of vibrational excitation for specific isomers and conformers. The implications of these observations for the dynamics of the state will be discussed.     

Spatially resolved concentration studies of ground state atoms in a flame: saturated absorption spectroscopic method

The authors describe the application of the saturated absorption spectroscopic method, introduced by Goldsmith, Optics Letters6, 525 (1981), to the determination of spatially resolved concentrations of ground state atoms in a flame. In the described version of the method, the beam of a single pulsed dye laser is divided into a probing and a disturing (= saturating beam), which intersect in a small volume of the flame. The perturbance of the probing beam by the saturating beam is a function of the concentration of the absorbing species. The authors foresee this method to become an important tool for flame and plasma diagnostic studies.     

The molecular structure and a Renner-Teller analysis of the ground and first excited electronic states of the jet-cooled CS2 + molecular ion

The A 2Pi(u) - X 2Pi(g) electronic band system of the jet-cooled CS2 + ion has been studied by laser-induced fluorescence and wavelength-resolved emission techniques. The ions were produced in a pulsed electric discharge jet using a precursor mixture of carbon disulfide vapor in high-pressure argon. Rotational analysis of the high-resolution spectrum of the 2Pi32 component of the 0(0) 0 band gave linear-molecule molecular structures of r0" = 1.5554(10) A and r0' = 1.6172(12) A. Renner-Teller analyses of the vibronic structure in the spectra showed that the ground-state spin-orbit splitting (A = -447.0 cm(-1)) is much larger than that of the excited state (A = -177.5 cm(-1)), but that the Renner-Teller parameters are of similar magnitude and that a strong nu1 - 2nu2 Fermi resonance occurs in both states. Previous analyses of the vibronic structure in the ground and excited states of the ion from pulsed field-ionization-photoelectron data are shown to be substantially correct.     

Analysis of the vibronic fine structure in circularly polarized emission spectra from chiral molecular aggregates

Using a Frenkel-exciton model, the degree of circular polarization of the luminescence (g(lum)) from one-dimensional, helical aggregates of chromophoric molecules is investigated theoretically. The coupling between the electronic excitation and a local, intramolecular vibrational mode is taken into account. Analytical expressions for the fluorescence band shape and g(lum) are presented for the case of strong and weak electronic coupling between the chromophoric units. Results are compared to those from numerical calculations obtained using the three particle approximation. g(lum) for the 0-0 vibronic band is found to be independent of the relative strength of electronic coupling between chromophores and excitation-vibration coupling. It depends solely on the number of coherently coupled molecules. In contrast, for the higher vibronic transitions[g(lum)] decreases with decreasing strength of the electronic coupling. In the limit of strong electronic coupling, [g(lum)] is almost constant throughout the series of vibronic transitions but for weak coupling [g(lum)] becomes vanishingly small for all vibronic transitions except for the 0-0 transition. The results are interpreted in terms of dynamic localization of the excitation during the zero point vibrational motion in the excited state of the aggregate. It is concluded that circular polarization measurements provide an independent way to determine the coherence size and bandwidth of the lowest exciton state for chiral aggregates.     

Spatially resolved concentration studies of ground state atoms and ions in an ICP: saturated absorption spectroscopic method

The saturated absorption spectroscopic method allows the direct determination of spatial distributions of absorbing species m a plasma to be made. Unlike most other emission and absorption methods which assume radial symmetry and require tedious Abel inversions, this method can be used regardless of the plasma symmetry because of its high spatial resolution. These characteristics are demonstrated with a 27.2 MHz ICP, utilizing short and long torches at power levels of 1.25 kW and 500 W for emission and fluorescence configurations, respectively. Distributions of Sr ground state atoms as well as Ba ground state ions were obtained under various conditions, using a single pulsed dye laser output as the spectroscopic probe in this diagnostic method.     

Single vibronic level photochemistry of NO2 in the 2491 Å system

A photochemical decomposition study of NO₂(B?²B₂) in specified vibronic states is reported. The O(¹D)-atom yields below and above the dissociation limit (40973 cm^?1) have been measured. The role played by the rotational excitation energy and the vibrational excitation modes in promoting the predissociation is discussed.     

The vibrational ground state rotational spectroscopic constants and structure of the HCN dimer

Rotational spectra have been assigned for four isotopic species of the linear HCN dimer in the vibrational ground state. The spectroscopic constants are

     

19.

Theoretical studies on the potential energy surface and rovibrational states for the electronic ground state of carbonyl sulfide     

Daiqian Xie  Yuhui Lu  Dingguo Xu  Guosen Yan 《Chemical physics》2001,270(3):6142-428

A potential energy surface for the electronic ground state of carbonyl sulfide was optimized by using a self-consistent field-configuration interaction method and involving the recent observed vibrational band origins up to 8000 cm⁻¹ for the Σ state. The root mean square error for this refinement was found to be 0.27 cm⁻¹. The calculated quartic force constants from the refined potential are very close to the recent high level ab initio calculations. The vibrational energy levels for the Π and Δ states and for some isotopomers of carbonyl sulfide molecule were calculated to test the refined potential. The calculated energy levels are in good agreement with the experimental values.     

20.

Microwave-optical double resonance in thioformaldehyde: Further studies of high rovibronic levels of the ground state     

《Chemical physics letters》1986,124(5):406-408

Microwave-optical double resonance experiments have been carried out on the J_O,J rotational levels of the 4¹ ùA₂ excited state of thioformaldehyde (H₂CS). The number of microwave transitions to high rovibronic levels of the ground state observed in a given frequency range increases in a roughly linear manner with J, supporting the proposition that K_a is not a good quantum number for these high rovibronic levels.     

isotope	-B0 (MHz)	DJ (kHz)	xN1 (MHz)	xN2 (MHz)
HC14N-HC14N	1745.80973(50)	2.133(30)	?4.0973(200)	?4.4400(190)
HC14N-HC15N	1700.30190(30)	1.939(40)	?4.1059(10)	-
HC15N-HC14N	1729.92082(20)	2.023(30)	-	?4.4339(6)
HC15N-HC15N	1684.28825(25)	1.900(30)	-	-

Theoretical studies on the potential energy surface and rovibrational states for the electronic ground state of carbonyl sulfide

A potential energy surface for the electronic ground state of carbonyl sulfide was optimized by using a self-consistent field-configuration interaction method and involving the recent observed vibrational band origins up to 8000 cm⁻¹ for the Σ state. The root mean square error for this refinement was found to be 0.27 cm⁻¹. The calculated quartic force constants from the refined potential are very close to the recent high level ab initio calculations. The vibrational energy levels for the Π and Δ states and for some isotopomers of carbonyl sulfide molecule were calculated to test the refined potential. The calculated energy levels are in good agreement with the experimental values.     

Microwave-optical double resonance in thioformaldehyde: Further studies of high rovibronic levels of the ground state

Microwave-optical double resonance experiments have been carried out on the J_O,J rotational levels of the 4¹ ùA₂ excited state of thioformaldehyde (H₂CS). The number of microwave transitions to high rovibronic levels of the ground state observed in a given frequency range increases in a roughly linear manner with J, supporting the proposition that K_a is not a good quantum number for these high rovibronic levels.