Difluorocarbene Studied with Threshold Photoelectron Spectroscopy (TPES): Measurement of the First Adiabatic Ionization Energy (AIE) of CF₂

Abstract

The first photoelectron band of difluorocarbene CF(2), has been studied by threshold photoelectron (TPE) spectroscopy. CF(2) was prepared by microwave discharge of a flowing mixture of hexafluoropropene, C(3)F(6), and argon. A vibrationally resolved band was observed in which at least twenty-two components were observed. In the first PE band of CF(2), the adiabatic ionization energy differs significantly from the vertical ionization energy because, for the ionization CF(2) (+) (X(2)A(1))+e(-) <-- CF(2) (X(1)A(1)), there is an increase in the FCF bond angle (by approximately 20 degrees ) and a decrease in the C--F bond length (by approximately 0.7 A). The adiabatic component was not observed in the experimental TPE spectrum. However, on comparing this spectrum with an ab initio/Franck-Condon simulation of this band, using results from high-level ab initio calculations, the structure associated with the vibrational components could be assigned. This led to alignment of the experimental TPE spectrum and the computed Franck-Condon envelope, and a determination of the first adiabatic ionization energy of CF(2) as (11.362+/-0.005) eV. From the assignment of the vibrational structure, values were obtained for the harmonic and fundamental frequencies of the symmetric stretching mode (nu(1)') and symmetric bending mode (nu(2)') in CF(2) (+) (X(2)A(1)).

Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators

“…Unlike monofluoroethene, however, the positively charged fragment first seen resulting from CQC cleavage is not the fluorine-containing moiety, but CH 2 + . This observation is explained by the 1.3 eV difference between the IE of these fragments (CH 2 52 10.39 AE 0.01 eV, CHF 53 10.06 AE 0.05 eV, and CF 2 54 11.36 AE 0.005 eV). Based on energetics considerations, the second rise in the CF + signal at 19 eV is suggested to stem mostly from the C-C bond cleavage in the H-loss fragment ion, HFCQCF + (calculated onset is 18.96 eV).…”

“…This is in close agreement to the Burcat value of 1121.9 AE 0.9 kJ mol À1 at 0 K, 42 though some distance from the Lias and JANAF values of 1131.0 and 1140.0 AE 0.5 kJ mol À1 respectively. 49,67 Using the C 2 F 4 -CF 2 + + CF 2 + e À E 0 value of 14.16 AE 0.04 eV, the IE of CF 2 of 11.362 AE 0.03 eV 54 and D f H o 0 K (C 2 F 4 ) of À669.4 AE 3.3 kJ mol À1 , 66 we obtain D f H o 0 K (CF 2 ) = À199.7 AE 5.6 kJ mol À1 . This value may be compared with previous values: À182.5 AE 6.3 kJ mol À1 (JANAF), 67 À185.3 AE 4.2 kJ mol À1 (Berman), 71 À191.7 AE 1.3 kJ mol À1 (Burcat), 42 À195.0 AE 2.9 kJ mol À1 (Dixon and Feller) 69 and À205.0 kJ mol À1 (Lias).…”

A Study of H2O2 with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE)

“…28−36 This spectrometer has been modified to allow TPE spectra to be obtained. 32,33 In order to record TPE spectra, the photoelectron spectrometer was tuned to detect near-zero energy (threshold) photoelectrons. The detection of threshold electrons was optimized using the Ar + ( 2 P 3/2 , 2 P 1/2 ) ← Ar( 1 S 0 ) (3p −1 ) TPE spectrum.…”

Photoionization of iodine atoms: Angular distributions and relative partial photoionization cross-sections in the energy region 11.0–23.0 eV

“…[19][20][21][22][23] The photoelectron spectrometer used was specifically designed to study reactive intermediates with PE, threshold photoelectron ͑TPE͒, and CIS spectroscopies using synchrotron radiation. 19,[23][24][25] Measurements were carried out either by recording PE spectra, in which the photon energy is fixed, or by recording CIS spectra, where the intensity of a particular atomic band is monitored as a function of photon energy. Both CIS and PE spectra were recorded in constant pass energy mode, by scanning the voltage on the lens which accelerates ͑or decelerates͒ the photoelectrons before they enter the energy analyzer.…”