Absolute Photoabsorption Oscillator Strengths Research Articles

Excitation Energies and Photoabsorption Oscillator Strengths of the Rydberg Series in CF3Cl. A Linear Response and Quantum Defect Study

Vertical excitation energies of the CF(3)Cl molecule have been obtained from a response function approach with a CC reference function to determine absolute photoabsorption oscillator strengths in the molecular-adapted quantum defect orbital formalism (MQDO). The present work covers more highly excited Rydberg states than have been experimentally reported. Assessing of the reliability of the present calculations is provided through a comparative analysis between the results of the molecule and the Cl atom. This can be used to allow for predictions of the same type of properties in other analogous systems.

Lower Rydberg series of methane: A combined coupled cluster linear response and molecular quantum defect orbital calculation

Vertical excitation energies as well as related absolute photoabsorption oscillator strength data are very scarce in the literature for methane. In this study, we have characterized the three existing series of low-lying Rydberg states of CH4 by computing coupled cluster linear response (CCLR) vertical excitation energies together with oscillator strengths in the molecular-adapted quantum defect orbital formalism from a distorted Cs geometry selected on the basis of outer valence green function calculations. The present work provides a wide range of data of excitation energies and absolute oscillator strengths which correspond to the Rydberg series converging to the three lower ionization potential values of the distorted methane molecule, in energy regions for which experimentally measured data appear to be unavailable.

Quantitative photoabsorption of methyl propyl ether in the UV, VUV and soft X-ray regions (5–200 eV)

Absolute photoabsorption oscillator strengths (cross-sections) in the valence-shell discrete and continuum regions methyl propyl ether CH3OC3H7 have been measured from 5 to 32 eV using high-resolution (∼0.05 eV fwhm) dipole (e,e) spectroscopy. Wide-range spectra, spanning the UV, VUV and soft X-ray regions, have also been obtained at low-resolution (∼1 eV fwhm) from 5 to 200 eV for methyl propyl ether, and these wide-range spectra have been used to determine the absolute oscillator strength scales by employing valence-shell TRK (i.e., S(0)) sum-rule normalization. Evaluations of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data give a static dipole polarizability for methyl propyl ether in good agreement with previously reported polarizability values. Other dipole sums S(u), (u=−1,−3,−4,−5,−6,−8,−10), and logarithmic dipole sums L(u), (u=−1 to −6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum-rules. The presently reported absolute photoabsorption oscillator strength data for methyl propyl ether (and all other atoms and molecules we have studied) are web-accessible at ftp.chem.ubc.ca/pub/cooper.

Quantitative photoabsorption of diethyl ether in the valence and carbon 1s inner shell regions (5–360 eV)

Abstract Absolute photoabsorption oscillator strengths (cross-sections) in the valence-shell discrete and continuum regions of diethyl ether C2H5OC2H5 have been measured from 5 to 32 eV using high-resolution (HR) (∼0.05 eV fwhm) dipole (e,e) spectroscopy. Wide-range spectra, spanning the UV, VUV and soft X-ray regions, have also been obtained at low-resolution (LR) (∼1 eV fwhm) from 5 to 360 eV which covers the valence-shell and C 1s inner-shell regions. The LR spectrum has been used to determine the absolute oscillator strength scale by employing valence-shell TRK (i.e., S(0)) sum-rule normalization. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for diethyl ether in good agreement with previously reported polarizability values obtained by other methods. Other dipole sums S(u), (u=−1,−3,−4,−5,−6,−8,−10), and logarithmic dipole sums L(u), (u=−1 to −6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum-rules. The presently reported absolute photoabsorption oscillator strength data are web-accessible at ftp.chem.ubc.ca/pub/cooper.

Absolute photoabsorption cross-sections (oscillator strengths) for ethanol (5–200 eV)

Absolute photoabsorption oscillator strengths (cross-sections) in the valence-shell discrete and continuum regions of ethanol (C 2H 5OH) have been measured from 5 to 32 eV using high-resolution (∼0.05 eV fwhm) dipole (e,e) spectroscopy. A wide-range spectrum, spanning the UV, VUV and soft X-ray regions, from 5 to 200 eV has also been obtained at low-resolution (∼1 eV fwhm), and this has been used to determine the absolute oscillator strength scale by employing valence-shell TRK (i.e., S(0)) sum-rule normalization. The presently reported high- and low-resolution absolute photoabsorption oscillator strengths are compared with previously published data from direct photoabsorption measurements in those limited energy regions where such data are available. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for ethanol in excellent agreement (within 0.5%) with previously reported polarizability values. Other dipole sums S( u), ( u=−1,−3,−4,−5,−6,−8,−10), and logarithmic dipole sums L( u), ( u=−1 to -6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum-rules.

Electronic excitation and optical cross sections of methylamine and ethylamine in the UV–VUV spectral region

High resolution UV–VUV photon absorption spectra of methylamine and ethylamine have been recorded between 5.0–9.0 eV (250–140 nm) using synchrotron radiation. In methylamine, the energies of the absorption bands are confirmed as centered at 5.7, 7.2, and 8.7 eV, respectively. In ethylamine the band centers are 5.8, 7.0, and 7.9 eV, respectively; the last band is seen here for the first time. Most of the transitions exhibit rich fine structure dominated by vibrational progressions involving excitation of an amino wagging vibration. The absolute photoabsorption oscillator strengths have been measured by photon absorption over the 5–9 eV range and by dipolar electron energy loss spectroscopy from 5–14 eV (250–90 nm).

Measurement of absolute dipole oscillator strengths for pyridine: photoabsorption and the molecular and dissociative photoionization in the valence shell (4–200 eV)

Absolute photoabsorption oscillator strengths for the valence shell of pyridine have been measured using dipole (e,e) spectroscopy at high resolution (∼0.05 eV FWHM) and low resolution (∼1 eV FWHM) from 4 to 30 eV and from 5 to 200 eV, respectively. The absolute photoabsorption oscillator strength scale (±5%) has been determined using valence shell TRK (i.e. S(0)) sum-rule normalization. The accuracy of the absolute scale has been verified using the S(−2) sum rule and literature values of the dipole polarizability. The low resolution photoabsorption results have been combined with time of flight mass spectral data measured using dipole (e,e+ion) coincidence spectroscopy (∼1 eV FWHM), to determine the absolute oscillator strengths for the molecular and dissociative photoionization of pyridine at equivalent photon energies from the first ionization threshold up to 60 eV.

Dipole (e,e+ion) spectroscopic studies of benzene: absolute oscillator strengths for molecular and dissociative photoionization in the VUV and soft X-ray regions

The branching ratios for molecular and dissociative photoionization of benzene (C 6H 6) have been measured in the VUV and soft X-ray regions using dipole (e,e+ion) coincidence spectroscopy (∼1 eV FWHM) at equivalent photon energies from the first ionization threshold up to 80 eV. The absolute partial oscillator strengths (cross-sections) for molecular and dissociative photoionization have been determined by combining previously reported absolute photoabsorption oscillator strength data [J. Electron Spectrosc. Relat. Phenom. 123 (2–3) (2002) 211–223] together with the photoionization branching ratios and the (multi-dissociative-corrected) photoionization efficiency obtained from time-of-flight mass spectra reported in the present work. The fact that the photoionization efficiency has been measured as greater than unity above ∼25 eV indicates the existence of multi-dissociative products from Coulomb explosion of multiply charged ions. Appearance potentials of all ion products from benzene are also reported. The presently reported results are compared with the previously published data where possible.

Dipole (e,e) spectroscopic studies of benzene: quantitative photoabsorption in the UV, VUV and soft X-ray regions

Absolute UV and VUV photoabsorption oscillator strengths (cross sections) for the valence shell discrete and continuum regions of benzene (C 6H 6) have been measured from 4 to 56 eV using high resolution (∼0.05 eV fwhm) dipole (e,e) spectroscopy. A wide-range spectrum, spanning the UV, VUV and soft X-ray regions, from 5 to 200 eV has also been obtained at low resolution (∼1 eV fwhm), and this has been used to determine the absolute oscillator strength scale by employing valence shell TRK [i.e., S(0)] sum-rule normalization. The presently reported high and low resolution absolute photoabsorption oscillator strengths are compared with previously published data from direct photoabsorption measurements in those limited energy regions where such data are available. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for benzene in good agreement (within ∼3.4%) with published polarizability values obtained from optical measurements. Other dipole sums S( u), ( u=−1, −3, −4, −5, −6, −8, −10), and logarithmic dipole sums L( u), ( u=−1 to −6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum-rules.

Ionic photofragmentation and photoionization of dimethyl ether in the VUV and soft X-ray regions (8.5–80 eV) – absolute oscillator strengths for molecular and dissociative photoionization

The branching ratios for molecular and dissociative photoionization of dimethyl ether (CH 3OCH 3, DME) have been measured in the VUV and soft X-ray regions using dipole (e,e+ion) coincidence spectroscopy (∼1 eV FWHM) at equivalent photon energies from the first ionization threshold up to 80 eV. The absolute partial oscillator strengths (cross-sections) for molecular and dissociative photoionization have been determined from recently published absolute photoabsorption oscillator strength data [R. Feng, G. Cooper, C.E. Brion, Chem. Phys. 260 (2000) 391] together with the photoionization branching ratios and the (multi-dissociative-corrected) photoionization efficiency obtained from time-of-flight mass spectra reported in the present work. No stable multiply charged molecular ion(s) from DME have been found in the present work. However, the fact that the photoionization efficiency has been measured as greater than unity above ∼30 eV indicates the existence of multi-dissociative products from Coulomb explosion of multiply charged ions. Appearance potentials of all ion products from DME are also reported. The presently reported results are compared with the previously published data where possible.

UV, VUV and soft X-ray photoabsorption of dimethyl ether by dipole (e,e) spectroscopies

Absolute UV and VUV photoabsorption oscillator strengths (cross-sections) for the valence shell discrete and continuum regions of dimethyl ether (CH 3OCH 3, DME) have been measured from 5 to 32 eV using high resolution (HR) (∼0.05 eV f.w.h.m.) dipole (e,e) spectroscopy. A wide-range spectrum, spanning the UV, VUV and soft X-ray regions, from 5 to 200 eV has also been obtained at low resolution (LR) (∼1 eV f.w.h.m.), and this has been used to determine the absolute oscillator strength scale by employing valence shell Thomas–Reiche–Kuhn (i.e., S(0)) sum-rule normalization. The presently reported HR and LR absolute photoabsorption oscillator strengths are compared with previously published data from direct photoabsorption measurements in those limited energy regions where such data are available. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for dimethyl ether in excellent agreement (within 0.5%) with previously reported polarizability values. Other dipole sums S( u), ( u=−1,−3,−4,−5,−6,−8,−10), and logarithmic dipole sums L( u), ( u=−1 to −6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum rules.

Dipole (e,e+ ion) coincidence studies of the ionic photofragmentation and photoionization of carbonyl sulfide in the valence shell and S 2p, 2s and C 1s inner shell regions (10–300 eV)

The branching ratios for molecular and dissociative photoionization of carbonyl sulfide (OCS) in the valence shell continuum regions and the inner shell (S 2p, 2s and C 1s) regions have been determined using dipole (e,e+ ion) coincidence spectroscopy (∼1 eV FWHM) at equivalent photon energies from the first ionization threshold up to 300 eV. The absolute partial oscillator strengths for molecular and dissociative photoionization have also been determined from recently published absolute photoabsorption oscillator strength data (R. Feng, G. Cooper, C.E. Brion, Chem. Phys. 252 (2000) 359) together with photoionization branching ratios and the (multi-dissociative-corrected) photoionization efficiency obtained from time-of-flight mass spectra reported in this work. The doubly charged molecular ion (OCS 2+) and its dissociation products (mainly OC +, S +, O + and C +) have also been studied in this work. Much higher relative abundances of these products have been found above the S 2p ionization edge (170.72 eV), which is due to Auger processes combined with Coulomb explosion. The presently reported results have been compared with previously published data where possible.

Quantitative studies of the photoabsorption of carbonyl sulphide in the valence-shell, S 2p, 2s and C 1s inner-shell regions (4–360 eV) by dipole electron impact spectroscopies

Electronic excitation spectra and absolute photoabsorption oscillator strengths (cross-sections) have been measured in the UV, VUV and soft X-ray energy regions for the valence- and inner- (S 2p, 2s, C 1s) shell photoabsorption of carbonyl sulphide (OCS) from 5 to 360 eV using low-resolution (∼1 eV fwhm) dipole (e, e) spectroscopy. The absolute oscillator strength scale has been determined using valence-shell TRK (i.e., S(0)) sum-rule normalization. The discrete structures, as well as the continuum structures, in the valence region also have been studied at high resolution (∼0.05 eV fwhm) from 4 to 32 eV. The presently reported high- and low-resolution absolute photoabsorption oscillator strengths are compared with previously published data (from the direct photoabsorption measurements) in those limited energy regions where such data exist. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for carbonyl sulphide in excellent agreement (within 2%) with previously reported polarizability values. Other dipole sums S( u) ( u=−1, −3 to −6, −8, −10) and logarithmic dipole sums L( u) ( u=−1 to −6) are also determined from the presently reported absolute differential photoabsorption oscillator strength data.

Absolute oscillator strengths for hydrogen sulphide: II. Ionic photofragmentation and photoionization in the valence shell continuum regions (10–60 eV)

Absolute oscillator strengths (cross sections) of ionic photofragmentation and photoionization for hydrogen sulphide in the valence shell continuum regions have been determined using dipole (e,e+ion) coincidence spectroscopy (∼1 eV fwhm) at equivalent photon energies from the first ionization threshold to 60.2 eV. These have been determined from the recently published absolute photoabsorption oscillator strengths [Feng et al., Chem. Phys. 244 (1999) 127] together with the photoionization efficiency and ionic photofragmentation branching ratios obtained from time-of-flight mass spectra reported in the present work. Consideration of the presently reported data together with the photoelectron branching ratios for H 2S and ionization potentials obtained from previously reported photoelectron and dipole (e,2e) spectroscopies yields quantitative information on the breakdown pathways of H 2S following absorption of radiation in the VUV and soft X-ray regions. A new photofragmentation product (H 2 +) and the doubly charged molecular ion (H 2S 2+) from hydrogen sulphide have been found in the present work. Partial photoionization oscillator strengths for production of the four valence shell electronic states of H 2S + have also been derived from the molecular and dissociative partial photoionization oscillator strengths over the entire energy range up to 60.2 eV.

Absolute oscillator strengths for hydrogen sulphide:: I. Photoabsorption in the valence-shell and the S 2p and 2s inner-shell regions (4–260 eV)

Absolute photoabsorption oscillator strengths (cross-sections) for the valence-shell discrete and continuum regions of hydrogen sulphide from 4 to 30 eV have been measured using high-resolution (∼0.05 eV fwhm) dipole (e, e) spectroscopy. A wide-range spectrum, covering both the valence shell and the S 2p and 2s inner shells, has also been obtained from 5 to 260 eV at low resolution (∼1 eV fwhm), and this has been used to determine the absolute oscillator strength scale using valence-shell TRK (i.e., S(0)) sum-rule normalization. The presently reported high- and low-resolution absolute photoabsorption oscillator strengths are compared with previously published data from direct photoabsorption measurements. In addition, a dipole sum-rule analysis on the present photoabsorption data has been performed. The static dipole polarizability for hydrogen sulphide determined from the S(−2) sum-rule using the presently reported oscillator strengths is compared with previously reported polarizability values. Other dipole sums S( u) ( u=−1, −3 to −6, −8, −10) and logarithmic dipole sums L( u) ( u=−1 to −6) are also determined from the presently reported absolute photoabsorption differential oscillator strengths.

Absolute photoabsorption oscillator strengths by electron energy loss methods: the valence and S 2p and 2s inner shells of sulphur dioxide in the discrete and continuum regions (3.5–260 eV)

Absolute photoabsorption oscillator strengths (cross-sections) for the valence shell discrete and continuum regions of sulphur dioxide from 3.5 to 51 eV have been measured using high resolution (∼0.05 eV FWHM) dipole ( e, e) spectroscopy. A wide-range spectrum, covering both the valence shell and the S 2p and 2s inner shells, has also been obtained from 5 to 260 eV at low resolution (∼1 eV FWHM), and this has been used to determine the absolute oscillator strength scale using valence shell TRK (i.e., S(0)) sum-rule normalization. The present measurements have been undertaken in order to investigate the recently discovered significant quantitative errors in our previously published low resolution dipole ( e, e) work on sulphur dioxide (Cooper et al., Chem. Phys. 150 (1991) 237; 150 (1991) 251). These earlier measurements were also in poor agreement with other previously published direct photoabsorption measurements. We now report new absolute photoabsorption oscillator strengths using both high and low resolution dipole ( e, e) spectroscopies. These new measurements cover a wider energy range and are much more consistent with the previously published direct photoabsorption measurements. The accuracy of our new measurements is confirmed by an S(−2) dipole sum-rule analysis which gives a static dipole polarizability for sulphur dioxide in excellent agreement (within 3.5%) with previously reported polarizability values. Other dipole sums S( u) ( u=−1,−3 to −6,−8,−10) and logarithmic dipole sums L( u) ( u=−1 to −6) are also determined from the presently reported absolute oscillator strength distributions.

Absolute oscillator strengths for the valence and inner (P 2p,2s) shell photoabsorption, photoionization, and ionic photofragmentation of PF 3

Absolute oscillator strengths (cross-sections) for the photoabsorption of phosphorus pentafluoride (PF 5) have been measured for the first time in the valence and phosphorus 2p discrete regions using high-resolution (0.0–0.1 eV fwhm), dipole ( e, e) spectroscopy. Long-range data (10–300 eV) have also been obtained at lower resolution (1 eV fwhm), from which the absolute oscillator strength scale has been determined using the valence-shell Thomas-Reiche-Kuhn sum-rule. The accuracy of the present measurement has been tested using the S(−2) sum rule normalization. Evaluation of the S(−2) sum using the presently reported absolute photoabsorption oscillator strength data gives a dipole polarizabilit for PF 5 in good agreement with the experimental value. The photoionization efficiencies, photoion branching ratios, and absolute partial oscillator strengths for molecular and dissociative photoionization have also been determined for PF 5 by dipole ( e, e+ion) coincidence spectroscopy from the first ionization threshold up to and above the phosphorus 2p edge.

Quantitative studies of the photoabsorption and photoionization of PCl 3 in the valence and inner (P 2p,2s; Cl 2p,2s) shell regions

Electronic excitation spectra and absolute photoabsorption oscillator strengths (cross sections) have been measured in the vacuum ultraviolet and soft X-ray energy regions for the valence and inner (P 2p,2s; Cl 2p,2s) shell photoabsorption of phosphorus trichloride (PCl 3) from 5 to 350 eV (1 eV fwhm) using dipole (e,e) spectroscopy. The discrete structures in the valence region and in the vicinity of the phosphorus 2p and chlorine 2p inner shells have also been studied at higher resolution (0.05–0.1 eV fwhm). Evaluation of the S(−2) sum using the presently reported absolute photoabsorption oscillator strength data gives a dipole polarizability for PCl 3 within 1% of the experimental value. The photoionization efficiency, ionic photofragmentation branching ratios, and absolute partial oscillator strengths for molecular and dissociative photoionization have also been determined for PCl 3 by dipole (e,e+ion) coincidence spectroscopy from the first ionization threshold up to the chlorine 2s edge.

Photoabsorption and photoionization of the valence and inner (P 2p, 2s) shells of PF 3: Absolute oscillator strengths and dipole-induced breakdown pathways

Absolute photoabsorption oscillator strengths (cross sections) for the valence and inner (P 2p, 2s) shells of phosphorus trifluoride (PF 3) have been measured using dipole ( e, e) spectroscopy in the 5–300 eV equivalent photon energy region (1 eV FWHM). The discrete spectral structures in the valence region and in the vicinity of the phosphorus 2p inner shell have also been studied at higher resolution (0.05 and 0.1 eV FWHM, respectively). Using these data and the S(−2) sum rule, the electric-dipole polarizability for PF 3 has been determined for the first time. In addition, dipole ( e, e+ion) coincidence spectroscopy has been used to obtain the photoionization efficiencies, photoion branching ratios, and absolute partial oscillator strengths for the molecular and dissociative photoionization channels of PF 3 from the first ionization threshold up to and above the phosphorus L shell edges to 175 eV. A consideration of the photoabsorption and photoionization measurement together with thermochemical data and results from previously published photoelectron branching ratios and photoelectron-photoion coincidence (PEPICO) studies provides information on the dipole-induced breakdown pathways of PF 3 in the photon region below 100 eV.

Ionic photofragmentation (11.5–160 eV) and PIPICO spectroscopy (40–130 eV) of BrCN in the valence shell and bromine 3d regions

Molecular and dissociative photoionization branching ratios and photofragment appearance potentials of BrCN have been determined using dipole (e, e + ion) spectroscopy at equivalent photon energies from the first ionization threshold up to 160 eV. Absolute partial photoionization oscillator strengths (cross sections) for the molecular and dissociative photoions have been obtained from the triple product of the photofragment branching ratio, the photoionization efficiency, and the previously reported absolute photoabsorption oscillator strength [Olney et al., Chem. Phys. 201 (1995) 505]. Information on the Coulomb explosion decay channels of doubly and triply charged molecular ions has been obtained from photoion-photoion coincidence (PIPICO) spectroscopy using synchrotron radiation as a light source in the 40–130 eV photon energy range. While stable doubly charged ions are formed in both the valence and the Br 3d regions no stable triply charged ions are observed. However, the PIPICO measurements detect time correlated singly and doubly charged fragment species resulting from Coulomb explosion of triply charged ions which are first formed at the Br 3d excitation threshold and throughout the ionization continuum by triple autoionization and double Auger type processes. The experimental results provide information on the dipole induced breakdown pathways resulting from valence shell and Br 3d ionization processes in BrCN.