Vibrational Levels Of Ground State Research Articles

Predissociation linewidths in O2 B 3Σu− (v=0,2)

Using laser-induced fluorescence techniques applied to Schumann–Runge absorption transitions from vibrationally excited O2(X3Σg−), we have measured the rotational and fine-structure level-specific linewidths in v=0 and v=2 of the B3Σu− state. These linewidths represent the first measurement of fine-structure level-specific predissociation rates in B3Σu−(v≤10), and they are found to vary considerably among the various rotational and fine-structure levels, encompassing a range of 0.09–0.34 cm−1 in v=0, N′≤36, and 0.4–1.4 cm−1 in v=2, N′≤24. Orbit-rotational coupling in the B3Σu−–3Πu interaction, in addition to spin-orbit coupling in the B3Σu−–1Πu, −3Πu, −5Πu interactions, is found to be crucial to explaining the relative predissociation rates among the fine-structure levels, even in low rotational levels. Measurements were made in the (v′,v″)=(0,9), (0,10), (0,21), (2,10), and (2,22) Schumann–Runge [B3Σu−(v′)←X3Σg−(v″)] bands without presumption as to the molecular constants in either the X or B states. The use of high ground state vibrational levels as a starting point for the photoexcitation measurements produces a spectral separation among the previously blended triplet components of the absorption lines. All lines in these bands are found to be broadened by predissociation, with those terminating in v′=0 and in the N′=J′−1 (F′1) levels exhibiting the smallest effect.

Stimulated-emission ion-dip spectra of phenol–H_2O hydrogen-bonded complex: estimation of intramolecular vibrational redistribution rates of ground-state vibrational levels

Stimulated-emission ion-dip spectroscopy was applied for the observation of the ground-state vibrational levels of jet-cooled phenol and its hydrogen-bonded complex with water. The observed ion-dip intensity, representing the stimulated emission from S1 to the vibrational level in S0 yields information about the intramolecular vibrational redistribution rate of the vibrational state. The intramolecular vibrational redistribution rate was estimated from the observed ion-dip intensities for the above species. It was found that a great enhancement of the intramolecular vibrational redistribution rate occurs with the formation of the hydrogen-bonded complex. The enhancement is ascribed to the increase of the density of the vibrational states contributed by the low-frequency hydrogen-bond modes.

Ion dip spectroscopy of van der Waals clusters

We report the implementation of ion dip spectroscopy in a supersonic molecular beam time-of-flight mass spectrometer as a powerful mass-selective method for observing ground-state vibrational levels in van der Waals clusters. Ion dip spectra of phenylacetylene and phenylacetylene-NH3 are demonstrated in the range of 900–1100 cm−1, showing prominent dips at 978.0, 1002.8, and 1028.0 cm−1. These dips have been tentatively assigned as 1301 3511, 1101 3510, and 3512, respectively, in phenylacetylene. Shifts in the 3512 and 11013510 vibrational bands of the complex are observed while the 13013511 band of the complex is either shifted or attenuated.

NO(B 2Π) radiative lifetimes: v=0–6

The zero-pressure radiative lifetime of the NO(B 2Π) state has been measured over the vibrational level range v=0–6. Laser-induced fluorescence was the technique chosen for this study, using two different sources of ground state NO. In one case, photodissociation of NO2 at 193 nm was used to obtain a range of ground state vibrational levels, from which selected rotational levels were then pumped to the B 2Π state, while in the second case, NO in v=0 was directly pumped. The two methods of preparing the excited state gave identical lifetime results. The data show a linearly decreasing lifetime with increasing vibrational level and to a good approximation the lifetimes, are given by τ(μs)=2.00–0.193v. Recent calculations for the B–X system show excellent agreement with experiment at low v, and an increasing discrepancy with increasing vibrational level, the experimental lifetimes decreasing more rapidly than the calculated ones. The lifetime values fall within the 0.85–2.0 μs range for v=0–6, and are substantially different from the 2–3 μs values that are currently quoted. Comparison of the new values with data derived from absorption studies shows good agreement even for the high vibrational levels. Absolute Einstein A factors are presented for the v′=6 progression.

Dissociation energy of the molecule AlBr from equilibrium measurements

The dissociation equilibrium AlBr=Al+Br was studied by effusion beam mass spectrometry over the range 1970 to 2260 K and the dissociation energy D00(AlBr) was derived as 4.41±0.06 eV. This value is in general agreement with other fragmentary thermochemical results, but it is lower than a value derived from a short extrapolation of vibrational levels in the excited 1π state, doubtless because of a potential maximum of about 0.22 eV in that state. A Birge–Sponer extrapolation of the ground state vibrational levels, when corrected for degree of ionicity, yields a D00 value in close accord with the experimental result, but an electrostatic model calculation falls short by 0.45 eV.

Laser Spectroscopy of Large Polyatomic Molecules in Supersonic Jets

Spectroscopic study of large polyatomic molecules had long been pre­ vented by spectral complexity. The complexity arises from the fact that a large molecule has a large number of vibrational degrees of freedom. Another complication comes from the thermal distribution of molecules over many ground-state vibrational levels, which causes many hot bands to appear in the spectrum. Molecular collisions in gas and condensed phases also contribute to broadening of spectral bands. All these com­ plicating factors become increasingly significant as a molecule becomes larger. Eventually, the spectrum becomes a continuous feature, even in the gas phase, owing to heavy spectral band congestion. A typical example of this spectral congestion is seen in the electronic absorption spectrum of biphenyl in the gas phase. The S 1 <So absorption spectrum of benzene is well known to exhibit prominent vibrational structure. However, in bi­ phenyl, which is composed of two benzene rings, the corresponding spec­ trum is completely structureless (1). We often encounter such a broad and structureless absorption spectrum when a molecule is larger than benzene. Clearly, detailed information on the energy levels cannot be obtained from such a broad spectrum. The recent development of the supersonic jet technique (2-5) has greatly improved the above situation. Supersonic expansion of sample molecules, seeded in high-pressure rare gas, into vacuum through a small nozzle

Autoionization from the lone-pair orbitals of molecules containing iodine

Autoionization to the lowest spin component of the ground state of the ion has been studied for the following alkyl iodides in the gas phase: CH3I, C2H5I, and nC3H7I. Measurements have been made using the constant ionic state (CIS) method for photon energies between the ionization potentials arising from the spin–orbit split lone-pair orbitals of iodine. To carry out the measurements, angle resolved photoelectron spectrometry has been coupled with a variable photon source extracted from synchrotron radiation. A series of broad resonances together with some sharp resonances are seen for each study and the results for each molecule in the series show strong similarity to one another, illustrating the localized atom-like character of the lone-pair orbital. There are strong differences found in the extent of the background, which is attributed to the higher density of states for the longer carbon chains. Most measurements were taken for the ground state vibrational level, but results are also presented for ionization to the ν2 excited vibrational state of CH3I+. New resonances, not seen for the ground vibrational state, are found and their origin discussed. CIS spectra on the I2 molecule are reported, which are in strong contrast to the alkyl iodides. Possible reasons for the differences are presented.

The UV absorption spectrum of C60 (buckminsterfullerene): A narrow band at 3860 Å

The absorption spectrum of the special C60 cluster buckminsterfullerene has been studied in a supersonic beam by laser depletion of the cold van der Waals complexes of C60 with benzene and methylene chloride. Both complexes were found to display a single, isolated absorption band in the near ultraviolet superimposed on a structureless absorption continuum. For the methylene chloride complex this feature is centered at 3860 Å, and is roughly 50 cm−1 wide. In the benzene van der Waals cluster, the corresponding feature is located at 3863 Å, and has a similar width. This spectrum is tentatively assigned to the 0–0 band of the lowest 1T1u←1Ag (LUMO+1←HOMO) transition of a truncated icosahedral carbon shell structure, broadened by coupling to the underlying quasicontinuum of ground state vibrational levels.

Photodissociation of nitrogen dioxide at 157.6 nm

The photodissociation of NO/sub 2/ has been studied at 157.6 nm, using an F/sub 2/ laser. The principal products are ground-state NO and 0, 4.8 eV of the available energy therefore being disposed on in translational, vibrational, and rotational energy. A total energy balance has not yet been performed, but NO vibrational levels have been detected by laser-induced fluorescence (LIF) in the B/sup 2/II-X/sup 2/II system in the range upsilon = 4-21; the thermodynamic limit is upsilon = 25. Extremely high rotational levels are found in all ground-state vibrational levels. In the most extensively studied level, upsilon = 5, most of the rotational population is to be found in the N = 50-70 region. Even at the highest vibrational levels, there is little nascent population at the bottom of the rotational manifold. Rotational relaxation of these high levels, where rotational quanta are typically 200 cm/sup -1/, occurs at approximately every collision with helium. NO(B-X) emission, independent of the LIF process, is quite strong and appears to be a consequence of resonances between the F/sub 2/ laser lines and transitions involving the nascent NO levels produced in the photodissociation. N/sub 2/(B/sup 3/II/sub g/-A/sup 3/..sigma../sub u//sup +/) emission is detected, possibly amore » result of N atom recombination; the most likely source of N atoms is photodissociation and/or photoionization of the excited NO product. Diffuse bands between 770 and 800 nm are also seen, but they have not yet been identified.« less

Solubility of H, D, and T in Pd at low concentrations.

The solubility measurements of H, D, and T in Pd in a large temperature range are presented. Analytic expressions are given for the equilibrium constants which describe the equilibria between hydrogen isotopes in the gas phase and hydrogen isotopes dissolved in a metal at infinite dilution. These expressions are used to predict the equilibrium constant for T in Pd from H and D data in Pd, and the predictions are compared to experimental observations. The Gibbs free energies, enthalpies, and entropies of solution of H, D, and T in Pd are calculated using these expressions. Contributions to these equilibrium constants from hydrogen isotopic species in the gas phase and the hydrogen isotopic species dissolved in Pd have been separated analytically. Parameters in these expressions, which are derived from isotope effects, define the ground-state energies of the H, D, and T species in Pd relative to the energy of atomic hydrogen at rest, i.e., the dissociation limit of ${\mathrm{H}}_{2}$, ${\mathrm{D}}_{2}$, and ${\mathrm{T}}_{2}$. The ground-state vibrational level for H in Pd was found to be 2322.6\ifmmode\pm\else\textpm\fi{}1.7 meV/atom below the dissociation limit for the diatomic molecule. For D in Pd the ground state was found to be 32.6\ifmmode\pm\else\textpm\fi{}1.1 meV/atom below that of H in Pd. The ground state for T in Pd was 46.6\ifmmode\pm\else\textpm\fi{}2.5 meV/atom below that of H in Pd. In addition, the partition functions for H, D, and T in Pd have been determined.

Calculated ground state potential surface and excitation energies for the copper trimer

The results of an SCF/SDCI treatment are presented for selected portions of the ground state potential energy surface for the Cu3 molecule. For equilateral triangle geometries (D3h) the lowest state is 2E′ arising from 4sa′214se′1. The 2E′ state exhibits strong Jahn–Teller distortion, leading to 2A1 (acute angle) and 2B2 (obtuse angle) minima in C2v symmetry. Here the 2B2 minimum is a true minimum on the surface while the 2A1 minimum is a saddle point or very shallow secondary minimum connecting adjacent 2B2 minima. This strong Jahn–Teller distortion is consistent with the observed ground state vibrational levels in the gas phase spectroscopic studies of Morse, Hopkins, Langridge-Smith, and Smalley and in the matrix Raman studies of Moskovits. The 2B2 minimum is also consistent with the observed ESR spectrum of Cu3 in a matrix, which has been interpreted as an obtuse angle structure with most of the spin density on the end Cu atoms. A linear 2Σ+u state is found to be 0.26 eV higher. Two possible candidates have been found for the upper state in the spectrum of Morse et al. (i) a 3s Rydberg state of 2A1 symmetry and (ii) a 3d→4s state of 2E″ symmetry. Both of these states are consistent with the observed selection rules. The 2E″ state would be expected to be weakly Jahn–Teller distorted in agreement with the fit to the upper state levels by Morse et al. and by Thompson, Truhlar, and Mead.

Ion dips in two-color photoionization spectra of jet-cooled trans-stilbene stimulated transitions to ground-state vibrational levels

The two-color photoionization spectra of jet-cooled trans-stilbene heve been measured. The ion dips appearing in the region above the adiabatic ionization potential were found to be due to the stimulated emission from the intermediate state to the ground-state vibrational levels. The observation of highly excited Rydberg states is also reported.

New chemical laser from the photodissociation of BrNO

NO laser emission from the photodissociation of BrNO has been observed between the ground state vibrational levels ′ = 7 and ′ = 3 using He and Br 2 as buffer gases. The laser threshold appears at > 5 torr with samples diluted (1:70) (BrNO:He) and reaches maximum intensity at ≈ 50 torr.

The vacuum uv emission spectrum of the 15N 22+ molecular ion

The vacuum uv emission of the 15N 2 2+ ion has been recorded for the first time. Rotational analysis of two bands, analogous to those already observed in the case of the natural isotope, confirm their assignment to the D 1Σ u +- X 1Σ g + (0, 0) and (1, 1) bands. More precise data are also obtained for the 3Σ g − state which perturbs ground state vibrational levels.

Threshold spectrum of CO2

A high-resolution threshold electron impact spectrometer is used to obtain a threshold spectrum of CO2 in the energy range from 3 to 20 eV. The dominant feature of the spectrum is the strong excitation of the unoccupied 2 pi u valence orbital from both 1 pi g and other deeper lying filled orbitals, giving rise to strong overlapping continua. A new, long vibrational progression in the bending mode is found, between 10 and 11 eV. The most prominent Rydberg series start above 12 eV and are associated with optically forbidden components of the transition to nd orbitals, not detected previously. Isoenergetic decay of the 2 Pi u resonance, populating the ground-state vibrational levels, is observed with an intensity comparable with the strongest electronic transitions. Strong resonant near-threshold excitation is found at 11.02 eV.

Interaction of low-energy electrons (1—30 eV) with condensed molecules: II. Vibrational-librational excitation and shape resonances in thinN2and CO films

Low-energy [(1-30)-eV] electron scattering in multilayer films of ${\mathrm{N}}_{2}$ and CO, and in Ar matrices containing ${\mathrm{N}}_{2}$, was investigated using high-resolution electron-energy-loss spectroscopy (HREELS) and one-dimensional multiple scattering theory. The films were formed by condensing the gases on a polycrystalline platinum substrate held near a temperature of 20 K. Comparisons of experimental electron-energy-loss spectra in the range 0-2.4 eV with those generated theoretically indicated that the former are composed of peaks which result from single and multiple vibrational losses broadened by multiple phonon losses. The excitation function of the $v=1\ensuremath{-}3$ vibrational levels of ground-state ${\mathrm{N}}_{2}$ and CO were measured under different film conditions and angles of incidence of the primary beam. In CO the excitation functions exhibited broad peaks at 2.5 and 20 eV due to the formation of $^{2}\ensuremath{\Pi}$ and $^{2}\ensuremath{\Sigma}$ transient anions, respectively, similar to those previously found in ${\mathrm{N}}_{2}$ films. From measurements of the intensity of the fundamental vibrational loss in ${\mathrm{N}}_{2}$ as a function of film thickness, the total cross section for excitation of all possible vibrational levels of ${\mathrm{N}}_{2}$ was found to be 3.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at resonance, and the sum of all phonon cross sections was found to be about 5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$.

Laser-induced fluorescence of CsH: The X 1Σ + state dissociation energy

Laser-induced fluorescence of CsH from the A 1Σ + electronic state to the X 1Σ + state was recorded using high-resolution Fourier transform spectrometry. Ground-state vibrational levels were observed from ν″ = 1 to the dissociation limit. These measurements showed anomalies in the X 1Σ + potential energy curve due to the avoided crossing of ionic and covalent potential curves. Accurate molecular constants were derived for the lower X 1Σ + vibrational levels. The observation of a quasibound level gave the first experimental determination of the dissociation energy (in cm −1): 14802 ⩽ D c ⩽ 14813.

Ground-State Vibrational Energy Levels of Polyatomic Transient Molecules

The experimentally determined ground-state vibrational energy levels of approximately 480 covalently bonded transient molecules possessing from 3 to 16 atoms are tabulated, together with references to the pertinent literature. The types of measurement surveyed include laser-based high resolution gas phase infrared absorption and visible-ultraviolet emission techniques, ultraviolet photoelectron spectroscopy, and matrix isolation spectroscopy. An assessment of the magnitude of the uncertainty of observations in neon, argon, and nitrogen matrices is given.

Excitation and dispersed fluorescence spectra of the 1B2(V)-1Σg+(X̄) transition of jet-cooled CS2

Abstract The fluorescence excitation and dispersed fluorescence spectra of the transition 1B2(V)-1Σg+(X) of jet-cooled CS2 have been measured. Vibrational analysis of the spectra has been carried out with the aid of ab initio calculations of the adiabatic potential in the excited state and of a Fermi resonance calculation of the ground-state vibrational levels. The calculated potential indicates a drastically bent structure in the excited state (θSCS = 131°±5°, RCS = 1.645±0.01 A) which explains the observed fluorescence spectra having extremely long progressions of the overtone of bending mode 2ν″2. The electronic origin of the transition has been found at 30530 cm−1 and the irregularly spaced vibronic levels in the excited state have been interpreted by a model potential V(θ) = − k2θ2 + k4θ4 along the bending coordinate θ with a central barrier height of 2000–2750 cm−1. The anomalous Franck-Condon intensity distribution of the fluorescence spectrum is also discussed in terms of the anharmonic potential and the nuclear coordinate dependence of the transition moment.

Laser spectroscopy of FeO: Rotational analysis of some subbands of the orange system

Extensive laser excitation spectra and rotationally resolved laser-induced fluorescence spectra have been recorded for the “orange system” of gaseous FeO in the wavelength regions 5790–6140 and 5580–5640 Å. Detailed rotational analyses have been performed for about 20 Ω′ substates lying between 16 350 and 18 550 cm −1. These are found to comprise a very severely perturbed 5Δ i excited electronic state with a bond length of about 1.69 Å (which is responsible for the parallel polarization of the electronic transition from the 5Δ i ground electronic state) and a large number of “extra” Ω substates with B′ values ranging from 0.38 to 0.50 cm −1, which almost certainly belong to high vibrational levels of lower-lying electronic states. Evidence about the natures of the “extra” states is confusing, however, with the 54FeO 56FeO isotope shifts apparently being in conflict with the patterns of vibrationally resolved laser-induced fluorescence. Every single Ω substate that has been analyzed shows rotational perturbations of varying severity. The density and magnitude of the rotational perturbations are quite exceptional for a diatomic molecule, and result in a new type of totally chaotic diatomic spectrum. There is a remarkable similarity to the visible spectrum of NO 2: in NO 2 the complications arise from the high density of perturbing ground state vibrational levels; in FeO there is a correspondingly high density of perturbing electronic states at lower energy. The great complexity of the FeO spectrum arises because the states are in an awkward intermediate spin-coupling case which still resembles Hund's case (a) but shows strong tendencies toward Hund's case (c) coupling.