Fernando Aguirre - Academia.edu (original) (raw)
Papers by Fernando Aguirre
The Journal of Physical Chemistry A, 2000
ABSTRACT Photofragment spectra of jet-cooled MCH2+ (M = Fe, Co, Ni) have been measured. Our inves... more ABSTRACT Photofragment spectra of jet-cooled MCH2+ (M = Fe, Co, Ni) have been measured. Our investigation of NiCH2+ represents the first reported spectroscopic study of this molecule. A spectroscopic threshold is observed for each of the three systems. In addition to imposing strict upper limits on the M+−CH2 bond strengths, these results further the discussion concerning the interpretation of spectroscopic thresholds as thermodynamic limits. The measured upper limits are: D°0(Fe+−CH2) ≤ 342 ± 2 kJ/mol, D°0(Co+−CH2) ≤ 331 ± 2 kJ/mol, and D°0(Ni+−CH2) ≤ 295 ± 5 kJ/mol. Three distinct, 2-nm-wide peaks are observed in the photofragment spectrum of CoCH2+, but the spectra lack sharp structure above threshold.
![Research paper thumbnail of The low-lying electronic states of FeO[sup +]: Rotational analysis of the resonance enhanced photodissociation spectra of the [sup 6]Π[sub 7/2]←X [sup 6]Σ[sup +] system](https://attachments.academia-assets.com/46817109/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/... more The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1 . The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ . The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
The journal of physical chemistry. A, Jan 26, 2006
The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging expe... more The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C3H3 radicals were performed, along with measurements of the Cl + C3H3 and HCl + C3H2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2P3/2) and Cl (2P1/2) (hereafter Cl) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 +/- 0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl+ mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the low-recoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C3+ ions in the mass spectrometer.
The Journal of Physical Chemistry A, 2000
... Kluwer Academic Publishers: Dordrecht, 1996. (21) Aguirre, F.; Husband, J.; Thompson, CJ; Met... more ... Kluwer Academic Publishers: Dordrecht, 1996. (21) Aguirre, F.; Husband, J.; Thompson, CJ; Metz, RB Chem. Phys. Lett. 2000, 318, 466−470. ... 28) Rodgers, MT;Ervin, KM; Armentrout, PB J. Chem. Phys. 1997, 106, 4499−4508. ...
The Journal of Physical Chemistry A, 2001
Solvated cluster ions Co 2+ (H 2 O) n with n ) 4-7 have been generated by electrospray ionization... more Solvated cluster ions Co 2+ (H 2 O) n with n ) 4-7 have been generated by electrospray ionization and studied by laser photofragment spectroscopy. The similarity between the spectrum of gas-phase Co 2+ (H 2 O) 6 and the absorption spectrum of aqueous cobalt(II) suggests that Co 2+ (H 2 O) 6 (aq) is responsible for the room-temperature solution absorption spectrum. The observed photodissociation spectrum of Co 2+ (H 2 O) 4 is similar to new bands which appear in aqueous cobalt(II) at high temperatures and have been assigned to Co 2+ (H 2 O) 4 (aq) by Swaddle and Fabes (Swaddle, T. W.; Fabes, L. Can. J. Chem. 1980Chem. , 58, 1418Chem. -1426. The hexahydrate was found to dissociate by loss of one or two water molecules, whereas the heptahydrate dissociates by loss of two or three water molecules. In both cases, loss of two water molecules is the preferred dissociation pathway. The tetrahydrate dissociates either by simple loss of water or by charge separation to form CoOH + (H 2 O) 2 and H 3 O + , with charge separation being the preferred dissociation channel. At 570 nm, photodissociation by charge separation leads to a kinetic energy release of 110 ( 20 kJ/mol, 48% of the available energy. This modest kinetic energy release is consistent with a "salt bridge" mechanism.
The Journal of Physical Chemistry A, 2000
... A 10 cm long home-built octopole ion guide 24,25 (E) leads the ions into an rf ion trap (RM J... more ... A 10 cm long home-built octopole ion guide 24,25 (E) leads the ions into an rf ion trap (RM Jordan Co., F). The ion trap serves to couple 26,27 the continuous ESI source to an existing pulsed (20 Hz) RTOF instrument that can also be used ... 22) Husband, J.; Aguirre, F.; Ferguson ...
![Research paper thumbnail of Vibrationally resolved photofragment spectroscopy of FeO[sup +]](https://attachments.academia-assets.com/46817108/thumbnails/1.jpg)
](The Journal of Chemical Physics, 1999
We report the first vibrationally resolved spectroscopic study of FeO ϩ . We observe the 0←0 and ... more We report the first vibrationally resolved spectroscopic study of FeO ϩ . We observe the 0←0 and 1←0 bands of a 6 ⌺←X 6 ⌺ transition at 28 648.7 and 29 311 cm Ϫ1 . Under slightly modified source conditions the 1←1 transition is observed at 28 473 cm Ϫ1 . In addition to establishing an upper limit D 0 o (Fe ϩ -O͒р342.7 kJ/mol, our results give the first experimental measurements of the vibrational frequencies in both the ground state, 0 Љϭ838Ϯ4 cm Ϫ1 , and the excited electronic state, 0 Јϭ662
![Research paper thumbnail of Electronic spectroscopy of intermediates involved in the conversion of methane to methanol by FeO[sup +]](https://attachments.academia-assets.com/46817110/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2002
Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction... more Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction, and photodissociation of the jet-cooled intermediates is examined in the visible and near-ultraviolet using time-of-flight mass spectrometry. The photodissociation spectrum of the aquo iron carbene complex ͓H 2 CvFe-OH 2 ͔ ϩ shows transitions to at least four excited electronic states in the FeCH 2 ϩ chromophore, with broad vibrational structure. Photoexcitation of the insertion intermediate ͓HO-Fe-CH 3 ͔ ϩ leads to formation of FeOH ϩ ϩCH 3 and also triggers the reaction to produce Fe ϩ ϩCH 3 OH. The photodissociation spectrum of ͓HO-Fe-CH 3 ͔ ϩ presents a vibrationally resolved band involving progressions in the excited state Fe-C stretch, Fe-O stretch, and O-Fe-C bend. The change in the Fe-C bond length in ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ upon photoexcitation is calculated from a Franck-Condon analysis of the vibronic features observed. The analysis of the experimental results is aided by hybrid Hartree-Fock/density-functional ͑B3LYP͒ calculations on ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ performed to determine molecular parameters, and time-dependent density functional theory ͑TD-DFT͒ calculations on FeCH 2 ϩ to predict excited electronic states.
Industrial & Engineering Chemistry Research, 1993
Chemical Physics Letters, 2001
... We first attempted to model the spectrum as a single vibrational progression, calculatingFran... more ... We first attempted to model the spectrum as a single vibrational progression, calculatingFranckCondon factors using Morse potentials for the ground and excited electronic states. FeS + ground-state parameters were fixed at the values calculated by Schröder et al. ...
Chemical Physics Letters, 2000
The photofragment spectra of jet-cooled and rotationally thermalized AuCH q are reported. Two cha... more The photofragment spectra of jet-cooled and rotationally thermalized AuCH q are reported. Two channels are observed: 2 loss of H and loss of CH with a branching ratio of 1.4:1 over the region studied. The presence of a threshold at 322 nm
The Journal of Physical Chemistry A, 2000
ABSTRACT Photofragment spectra of jet-cooled MCH2+ (M = Fe, Co, Ni) have been measured. Our inves... more ABSTRACT Photofragment spectra of jet-cooled MCH2+ (M = Fe, Co, Ni) have been measured. Our investigation of NiCH2+ represents the first reported spectroscopic study of this molecule. A spectroscopic threshold is observed for each of the three systems. In addition to imposing strict upper limits on the M+−CH2 bond strengths, these results further the discussion concerning the interpretation of spectroscopic thresholds as thermodynamic limits. The measured upper limits are: D°0(Fe+−CH2) ≤ 342 ± 2 kJ/mol, D°0(Co+−CH2) ≤ 331 ± 2 kJ/mol, and D°0(Ni+−CH2) ≤ 295 ± 5 kJ/mol. Three distinct, 2-nm-wide peaks are observed in the photofragment spectrum of CoCH2+, but the spectra lack sharp structure above threshold.
The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/... more The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1 . The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ . The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
The journal of physical chemistry. A, Jan 26, 2006
The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging expe... more The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C3H3 radicals were performed, along with measurements of the Cl + C3H3 and HCl + C3H2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2P3/2) and Cl (2P1/2) (hereafter Cl) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 +/- 0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl+ mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the low-recoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C3+ ions in the mass spectrometer.
The Journal of Physical Chemistry A, 2000
... Kluwer Academic Publishers: Dordrecht, 1996. (21) Aguirre, F.; Husband, J.; Thompson, CJ; Met... more ... Kluwer Academic Publishers: Dordrecht, 1996. (21) Aguirre, F.; Husband, J.; Thompson, CJ; Metz, RB Chem. Phys. Lett. 2000, 318, 466−470. ... 28) Rodgers, MT;Ervin, KM; Armentrout, PB J. Chem. Phys. 1997, 106, 4499−4508. ...
The Journal of Physical Chemistry A, 2001
Solvated cluster ions Co 2+ (H 2 O) n with n ) 4-7 have been generated by electrospray ionization... more Solvated cluster ions Co 2+ (H 2 O) n with n ) 4-7 have been generated by electrospray ionization and studied by laser photofragment spectroscopy. The similarity between the spectrum of gas-phase Co 2+ (H 2 O) 6 and the absorption spectrum of aqueous cobalt(II) suggests that Co 2+ (H 2 O) 6 (aq) is responsible for the room-temperature solution absorption spectrum. The observed photodissociation spectrum of Co 2+ (H 2 O) 4 is similar to new bands which appear in aqueous cobalt(II) at high temperatures and have been assigned to Co 2+ (H 2 O) 4 (aq) by Swaddle and Fabes (Swaddle, T. W.; Fabes, L. Can. J. Chem. 1980Chem. , 58, 1418Chem. -1426. The hexahydrate was found to dissociate by loss of one or two water molecules, whereas the heptahydrate dissociates by loss of two or three water molecules. In both cases, loss of two water molecules is the preferred dissociation pathway. The tetrahydrate dissociates either by simple loss of water or by charge separation to form CoOH + (H 2 O) 2 and H 3 O + , with charge separation being the preferred dissociation channel. At 570 nm, photodissociation by charge separation leads to a kinetic energy release of 110 ( 20 kJ/mol, 48% of the available energy. This modest kinetic energy release is consistent with a "salt bridge" mechanism.
The Journal of Physical Chemistry A, 2000
... A 10 cm long home-built octopole ion guide 24,25 (E) leads the ions into an rf ion trap (RM J... more ... A 10 cm long home-built octopole ion guide 24,25 (E) leads the ions into an rf ion trap (RM Jordan Co., F). The ion trap serves to couple 26,27 the continuous ESI source to an existing pulsed (20 Hz) RTOF instrument that can also be used ... 22) Husband, J.; Aguirre, F.; Ferguson ...
The Journal of Chemical Physics, 1999
We report the first vibrationally resolved spectroscopic study of FeO ϩ . We observe the 0←0 and ... more We report the first vibrationally resolved spectroscopic study of FeO ϩ . We observe the 0←0 and 1←0 bands of a 6 ⌺←X 6 ⌺ transition at 28 648.7 and 29 311 cm Ϫ1 . Under slightly modified source conditions the 1←1 transition is observed at 28 473 cm Ϫ1 . In addition to establishing an upper limit D 0 o (Fe ϩ -O͒р342.7 kJ/mol, our results give the first experimental measurements of the vibrational frequencies in both the ground state, 0 Љϭ838Ϯ4 cm Ϫ1 , and the excited electronic state, 0 Јϭ662
The Journal of Chemical Physics, 2002
Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction... more Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction, and photodissociation of the jet-cooled intermediates is examined in the visible and near-ultraviolet using time-of-flight mass spectrometry. The photodissociation spectrum of the aquo iron carbene complex ͓H 2 CvFe-OH 2 ͔ ϩ shows transitions to at least four excited electronic states in the FeCH 2 ϩ chromophore, with broad vibrational structure. Photoexcitation of the insertion intermediate ͓HO-Fe-CH 3 ͔ ϩ leads to formation of FeOH ϩ ϩCH 3 and also triggers the reaction to produce Fe ϩ ϩCH 3 OH. The photodissociation spectrum of ͓HO-Fe-CH 3 ͔ ϩ presents a vibrationally resolved band involving progressions in the excited state Fe-C stretch, Fe-O stretch, and O-Fe-C bend. The change in the Fe-C bond length in ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ upon photoexcitation is calculated from a Franck-Condon analysis of the vibronic features observed. The analysis of the experimental results is aided by hybrid Hartree-Fock/density-functional ͑B3LYP͒ calculations on ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ performed to determine molecular parameters, and time-dependent density functional theory ͑TD-DFT͒ calculations on FeCH 2 ϩ to predict excited electronic states.
Industrial & Engineering Chemistry Research, 1993
Chemical Physics Letters, 2001
... We first attempted to model the spectrum as a single vibrational progression, calculatingFran... more ... We first attempted to model the spectrum as a single vibrational progression, calculatingFranckCondon factors using Morse potentials for the ground and excited electronic states. FeS + ground-state parameters were fixed at the values calculated by Schröder et al. ...
Chemical Physics Letters, 2000
The photofragment spectra of jet-cooled and rotationally thermalized AuCH q are reported. Two cha... more The photofragment spectra of jet-cooled and rotationally thermalized AuCH q are reported. Two channels are observed: 2 loss of H and loss of CH with a branching ratio of 1.4:1 over the region studied. The presence of a threshold at 322 nm