Ágúst Kvaran

Spectroscopic characterization of the lowest singlet states of CdNe, CdAr, and CdKr

We report the characterization of the first excited singlet states of CdNe, CdAr, and CdKr, which correlate with Cd(5s5p 1P1) and the ground‐state rare‐gas atoms. The van der Waals molecules were created in a free jet supersonic expansion and studied by laser‐induced fluorescence, dispersed fluorescence, laser pump/probe action spectra, and spectral simulations. The C 1Π1 states are found to be more strongly bound than their triplet counterparts: 116Cd20Ne (De=89 cm−1, ωe=23.36 cm−1, ωexe=1.80 cm−1, re =3.61±0.05 A); 116Cd40Ar (De=544 cm−1, ωe=47.97 cm−1, ωexe=1.11 cm−1, re=3.28±0.05 A); 114Cd84Kr (De=1036 cm−1, ωe=56.72 cm−1, ωexe=0.81 cm−1, Δre(C 1Π–X 1Σ+) =1.16 A). This is attributed to spatial differences between the atomic p orbital of the singlet vs the triplet excited state of the Cd atom. The D 1Σ0+ states of CdAr and CdKr were found to be repulsive for Franck–Condon accessible internuclear distances. No production of Cd(5s5p 2PJ) states from predissociation of any C 1Π1 molecular state was observed.

Spectroscopic characterization of the X(10+) and A(30+) states of CdNe, CdAr, CdKr, and CdXe

We report the spectroscopic characterization of the X(10+) and A(30+) states of CdNe, CdAr, CdKr, and CdXe. The van der Waals molecules were created in a free jet supersonic expansion and studied by low and high resolution laser‐induced fluorescence. CdAr was also studied by dispersed fluorescence. A method of analyzing rotationally structured vibrational bands of overlapping isotopic spectral contributions is discussed. Spectroscopic parameters are obtained from computer simulations of CdNe and CdAr spectra and from analysis of vibrational isotope splittings for CdKr and CdXe. CdNe: r‘e (X state)=4.26±0.05 A, re(A state) =3.62±0.05 A, D’e(A state) =77 cm−1; CdAr: r‘e(X) =4.33±0.04 A, r’e(A) =3.45±0.03 A, De(A) =325 cm−1; CdKr: D’e(A) =513 cm−1 and CdXe: De(A) =1086 cm−1.

Conformational Properties of 1-Fluoro-1-silacyclohexane, C5H10SiHF: Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum Chemical Calculations†

The molecular structures of axial and equatorial conformers of 1-fluorosilacyclohexane, C5H10SiHF, as well as the thermodynamic equilibrium between these species were investigated by means of gas electron diffraction (GED), dynamic nuclear magnetic resonance, temperature-dependent Raman spectroscopy, and quantum chemical calculations (MP2, DFT, and composite methods). According to GED, the compound exists in the gas phase as a mixture of two conformers possessing the chair conformation of the six-membered ring and Cs symmetry and differing in the axial or equatorial position of the Si-F bond (axial ) 63(8) mol %/equatorial ) 37(8) mol %) at T ) 293 K, corresponding to an A value of –0.31(20) kcal mol. Density functional theory (DFT) calculations were employed to obtain the minimal energy path of the conformational inversion. The MP2, G3B3, and CBS-QB3 methods were also employed to calculate the equilibrium geometries and energies of the local minima in the gas phase and in solution. The gas-phase results are in good agreement with the experiment, whereas a combined PCM/IPCM(B3LYP/6-311G(d)) approach overestimates the stabilization of the axial conformer by 0.3-0.4 kcal mol in solution at 112 K. Temperature-dependent Raman spectroscopy in the temperature ranges of 210–300 K (neat liquid), 120–300 K (pentane solution), and 200–293 K (dichloromethane solution) also indicates that the axial conformer is favored over the equatorial one by 0.25(5), 0.22(5), and 0.28(5) kcal mol (∆H values), respectively.

(2+1) REMPI spectra of Ω=0 states of the hydrogen halides: Spectroscopy, perturbations and excitation mechanisms

(2+1) REMPI spectra of HX (X=Cl, Br and I) have been recorded and analyzed by simulation calculations to derive rotational constants, band origins and isotope shift values for a number of vibrational bands of Ω=0 states. Our data for HCl compare nicely with those derived by Green et al. by conventional analysis methods [D. S. Green et al., J. Mol. Spectrosc. 150, 303, 354, 388 (1991); D. S. Green and S. C. Wallace, J. Chem. Phys. 96, 5857 (1992)]. New spectroscopic parameters were derived for eight vibrational bands which are assigned to the V(1Σ+) state, for v′=4 of the E(1Σ+) state, as well as for five new bands in HBr. New spectroscopic parameters were derived for four vibrational bands which are assigned to the V state and for v′=1 of the E state in HI. Anomalies observed in energy level spacings, rotational parameters and isotope shift values are interpreted as being largely due to homogeneous interactions between the V and the E states. It is argued that the interaction causes a compression of rovib...

Resonance enhanced multiphoton ionization of the hydrogen halides: Rotational structure and anomalies in Rydberg and ion-pair states of HCl and HBr

(2+1) resonance enhanced multiphoton ionization spectra have been recorded, simulated, and used to derive energies of rovibrational levels in the F(1Δ), E(1Σ+), and V(1Σ+) states for HCl (H35Cl and H37Cl) and HBr (H79Br and H81Br). Spectroscopic parameters derived for the F states compare nicely with those derived by others using conventional analysis methods. Clear evidence for near resonance interactions between the F and the V states is seen for the first time, both in HCl and HBr. Shape of curves for rotational level energy spacings versus rotational quantum numbers are found to depend characteristically on the nature of off-resonance interactions observed between the E and the V states. Model calculations for state interactions, based on perturbation theory, are performed for HCl. These prove to be useful to interpret observed perturbations, both qualitatively and quantitatively. Interaction strengths are evaluated for F to V and E to V state interactions. Variations observed in the intensity ratios ...

Chemiluminescence of argon bromide. I. The emission spectrum of ArBr

In this first systematic study of the ArBr molecule, chemiluminescence spectra are generated by the reactions of metastable argon atoms with bromine‐containing compounds. Three continua, due to the B (1/2)−X (1/2), B (1/2)−A (1/2) and C (3/2)−A3/2) transitions are characterized, their pressure dependences examined, and the extent of their overlap discussed in some detail. From the temperture dependence of the spectra, an upper limit for the electronic energy of the B (1/2) state is derived: TeB?61 850 cm−1.

Reactions of Xe(3 P 2) and Xe(3 P 1) with HCl, HBr and HI; energy utilization, energy disposal, product rotational polarization and reaction dynamics

We report a systematic study of the reactions of Xe(3 P 1, 3 P 2) with HCl, HBr and HI using both spectroscopic and molecular beam techniques. No reaction is observed at room temperatures for Xe(3 P 2) with HCl; analysis of the Xe(3 P 1)/HCl data yields an estimate of the endoergicity of the 3 P 2 reaction which agrees within experimental error with the threshold obtained from deconvolution of the excitation function measured in the molecular beam experiments, thus indicating little or no barrier in the entrance channel. Surprisal analysis of the vibrational population distributions obtained by inversion of the rare gas halide spectra yields estimates for the fraction of the available energy disposal into vibration . The results are in broad agreement with earlier estimates and are roughly independent of the spin orbit component for a given reaction. Deviations from the purely kinematic limit in the product rotational alignment ( ) increase across the series HCl, HBr, HI while ...

Vibrational relaxation of KrF* and XeCl* by rare gases

A steady-state, chemiluminescence technique has been used to measure effective rate constants for vibrational relaxation as a function of vibrational level for KrF* in collisions with He, Ne, and Ar and XeCl* with Ar. The effective rate constants reported include contributions to relaxation due to intersystem crossing between theB andC states, in addition to direct relaxation within theB state. The relevance of these results to the understanding of previous measurements in KrF and XeCl lasers is discussed.

Threshold photoelectron spectroscopy of CF4 up to 60.5 eV

Abstract The threshold photoelectron spectrum of CF4 up to 60.5 eV has been recorded using synchrotron radiation and a penetrating-field electron spectrometer of high resolution. Our results confirm the broad spectral features of the X 2T1, A2T2 and B 2E state bands of CF4+ reported previously with He I PES. The influence of autoionizing super-excited states of CF4 has been observed as an extension of the high-energy tail of the B 2E state, as a structured band in the energy region between the B 2E and C 2T2 states, and as additional vibrational structure extending the D 2A1 state band. Improved spectra of the C 2T2 and D 2A1 states have been obtained as a consequence of the high resolution of this study. The overall electronic state band profiles observed here up to about 26eV agree with a recently published low-resolution threshold photoelectron spectrum of CF4 [Creasey et al., Chem. Phys., 174 (1993) 441]. Between 26 and 60.5 eV a continuum-like background was observed with some broad-band features superimposed on it. One broad peak, centered on 40.3 eV, is tentatively assigned to the formation of the Ẽ 2T2 and F 2A1 states of CF4+, but the formation of the double-charged ion, CF42+, may also be involved.

Analysis of the 350–400 nm oscillatory continuum from I2 (D 1Σ+u)

Abstract The 350–400 nm oscillatory continuum, observed in emission when I 2 is excited to the D 1 Σ + u state (λ = 193 nm, u′ ≈ 134), has been analysed. The lower potential state, which correlates with two ground-state 1 atoms, is found to be purely repulsive between 2.75 and 3.8 A, the range defined by the observed fluorescence. The band is partially overlapped by another system and there are two possible positions for the band origin, leading to very similar lower states.