Vacuum-UV fluorescence spectroscopy of PF3 in the range 9–20 eV

The Journal of Chemical Physics

Chim

Tuckett

et al. 2001

Self Cite

The vacuum-UV absorption and fluorescence spectroscopy of CF 2 X 2 (X=H,Cl,Br) in the range nm is reported. Tunable vacuum-UV radiation in the range 8-22 eV from synchrotron sources at either Daresbury, UK or BESSY1, Germany is used to excite the titled molecules. Fluorescence excitation spectra, with undispersed detection of the fluorescence, were recorded at Daresbury with a resolution of 0.1 nm. VUV absorption spectra at a resolution of 0.08 nm, and dispersed emission spectra with an optical resolution of 8 nm were recorded at BESSY1. Action spectra, in which the VUV energy is scanned with detection of the fluorescence at a specific wavelength, were also recorded at BESSY1 with a resolution of 0.3 nm ; appearance energies for production of a particular emitting state of a fragment are then obtained. Using the single-bunch mode of BESSY1, lifetimes of all emitting states that fall in the range ca. 3-80 ns have been measured. The peaks in the VUV absorption spectra of CF 2 X 2 are assigned to Rydberg transitions. For CF 2 H 2 below 11 eV, there is good agreement between the absorption and the fluorescence excitation spectra, whereas above 11 eV and for the whole range 8-22 eV for CF 2 Cl 2 and CF 2 Br 2 there is little similarity. This suggests that photodissociation to emitting states of fragment species represent minor channels. In the range 8-15 eV, emission is due mainly to CF 2 Ã 1 B 1 − X 1 A 1 and weakly to CFX Ã 1 A" − X 1 A'. These products form by photodissociation of Rydberg states of CF 2 X 2 , and the thresholds for their production therefore relate to energies of the Rydberg states of the parent molecule. For CF 2 H 2 below 11.8 eV CF 2 Ã 1 B 1 can only form with H 2 , whereas for CF 2 Cl 2 and CF 2 Br 2 it is not possible to say whether the other products are 2X or X 2 . For energies above ca. 15 eV, emission is due to diatomic fragments ; CF B 2 ∆ and A 2 Σ + , CCl A 2 ∆, CH B 2 Σ -and A 2 ∆, Cl 2 and Br 2 D' 2 3 Π g , and possibly CBr A 2 ∆. From their appearance energies, there is evidence that, with the exception of CF B 2 ∆ / CF 2 H 2 where the ground state of HF must form , the excited state of CF, CCl or CH forms in association with three atoms. Our results yield no information whether the three bonds in CF 2 X 2 * break simultaneously or sequentially. We suggest that the anomalous behaviour of CF 2 H 2 , in forming H-H or H-F bonds in unimolecular photofragmentation processes, relates to the small size of the hydrogen atom, and hence the unimportance of steric effects in the tightlyconstrained transition state. In no cases is emission observed from excited states of either the CF 2 X free radical or the parent molecular ion, CF 2 X 2 + .4

Section: Discussionmentioning

confidence: 98%

Vacuum–ultraviolet absorption and fluorescence spectroscopy of CF2H2, CF2Cl2, and CF2Br2 in the range 8–22 eV

The Journal of Chemical Physics

Chim

Tuckett

et al. 2001

Self Cite

“…460 nm, and assigned it to the c 1 [35]. This made it possible for the Ẽ − Ã , C − X , B − X and Ã − X transitions in PF 2 to be identified in the dispersed fluorescence spectra of PF 3 [1]. Since these calculations have not been performed for NF 2 , the emission bands cannot be assigned to particular transitions.…”

Section: Discussionmentioning

confidence: 99%

“…In a series of papers our group has shown that VUV fluorescence spectroscopy can be an extremely useful technique for probing both spectroscopic and dynamic behaviour of the Rydberg states of polyatomic molecules [e.g. 1,2]. Other groups, using high-energy electrons or radiofrequency (RF) discharges, have sought to diagnose the emissions which are produced following the VUV excitation of NF 3 [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The observation of fluorescence from excited states of NF2 and NF following the photodissociation of NF3 in the 11–30 eV range

Chemical Physics Letters

Tuckett

Jochims

et al. 2001

A study of the vacuum-ultraviolet (VUV) fluorescence spectroscopy of NF 3 in the 11-30 eV range is presented. Synchrotron radiation from BESSY1, Berlin provides the VUV excitation source. Emission due to NF bΣ -at 528.8 nm is observed between 11.5 and 21.0 eV.Other emissions, which are believed to be due to transitions between highly excited states of NF 2 , are observed at higher energies, 14.8-24.5 eV. Lifetimes associated with two of these bands at 325 nm and 410 nm are determined to be 12.9 and 13.0 ns, respectively. The similarity of the measured values implies that the two transitions originate from a common upper state. Seccombe et al. (2001) 3

“…In a series of papers [2][3][4][5][6] we have reported the observation and analysis of the non-dispersed fluorescence and dispersed emission spectra following VUV excitation of a range of halides of Groups III, IV and V of the Periodic Table . To date, we have performed experiments on BCl 3 [2], BBr 3 [3], CF 3 X (X F, Cl, Br, H) [4], SiF 4 [5] and PF 3 [6]. Many of these compounds are either used widely or are involved indirectly in the radiofrequency (RF) plasma etching of semiconductor devices.…”

Section: Introductionmentioning

confidence: 99%

Vacuum–UV fluorescence spectroscopy of CCl4, SiCl4 and GeCl4 in the range 9–25eV

Biehl

Boyle

Journal of Electron Spectroscopy and Related Phenomena

et al. 1998

Self Cite

The vacuum-ultraviolet (UV) and visible spectroscopy of MCl 4 (M C, Si, Ge) using fluorescence excitation and dispersed emission techniques is reported. Fluorescence excitation spectra have been recorded following photoexcitation with monochromatised synchrotron radiation in the vacuum-UV energy range 9-25 eV with an average resolution of ca. 0.06 eV. All the peaks in the Rydberg spectra that photodissociate to a fluorescing state of a fragment have been assigned. The Rydberg states arise predominantly from electron excitation from one of the Cl 3pp non-bonding molecular orbitals of MCl 4 , and quantum defects for the Rydberg states characteristic of a chlorine atom are obtained. Dispersed emission spectra in the UV/visible region have been recorded with an optical resolution of ca. 4-8 nm at the energies of the peaks in the excitation spectra. Five different decay channels are observed: (a) CCl 2 Ã1 B 1 -X1 A 1 fluorescence at ca. 420-600 nm from CCl 4 excited in the range 9-12 eV, (b) SiCl 2 /GeCl 2 ã3 B 1 -X1 A 1 and Ã1 B 1 -X1 A 1 fluorescence from SiCl 4 /GeCl 4 excited in the range 9-14 eV, (c) SiCl ϩ 4 =GeCl ϩ 4C2 T 2 -X2 T 1 and C2 T 2 -Ã2 T 2 fluorescence at ca. 350-700 nm from SiCl 4 /GeCl 4 for photon energies above the adiabatic ionisation energy of the C2 T 2 state of SiCl ϩ 4 =GeCl ϩ 4 (15.0 and 14.6 eV, respectively), (d) CCl A 2 D-X 2 P fluorescence at ca. 276-280 nm from CCl 4 excited in the range 14-18eV, and (e) Si* and Ge* atomic emission lines at wavelengths below 310 nm from SiCl 4 /GeCl 4 excited in the range 19-25 eV. These assignments are confirmed by action spectra in which the energy of the vacuum-UV radiation is scanned with detection of the fluorescence at a fixed, dispersive wavelength. By using the single-bunch mode of synchrotron radiation, lifetimes of all the emitting states that fall in the range ca. 4-100 ns have been measured. The MCl ‫ء‬ 2 products are formed by photodissociation of low-lying Rydberg states of MCl 4 ; the thresholds for their production therefore relate to energies of Rydberg states of the parent molecule. The CCl*, Si* and Ge* products are formed by sequential, multi-step photodissociation of MCl ‫ء‬ 2 ; the thresholds for these emissions correspond to the thermodynamic thresholds to form the emitting product with either three (in the case of CCl*) or four (in the case of Si*/Ge*) chlorine atoms.