ORCID Profile
0000-0001-5572-4784
Current Organisation
University of Massachusetts Boston
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Publisher: American Chemical Society (ACS)
Date: 15-02-2008
DOI: 10.1021/JA078342T
Abstract: The gas-phase laser-induced fluorescence (LIF) spectrum of a 1-phenylpropargyl radical has been identified in the region 20,800-22,000 cm(-1) in a free jet. The radical was produced from discharges of hydrocarbons including benzene. Disregarding C2, C3, and CH, this radical appears as the most strongly fluorescing product in a visible wavelength two-dimensional fluorescence excitation-emission spectrum of a jet-cooled benzene discharge. The structure of the carrier was elucidated by measurement of a matching resonant two-color two-photon ionization spectrum at m/z = 115 and density functional theory. The assignment was proven conclusively by observation of the same excitation spectrum from a low-current discharge of 3-phenyl-1-propyne. The apparent great abundance of the 1-phenylpropargyl radical in discharges of benzene and, more importantly, 1-hexyne may further underpin the proposed importance of the propargyl radical in the formation of complex hydrocarbons in combustion and circumstellar environments.
Publisher: American Chemical Society (ACS)
Date: 21-10-2006
DOI: 10.1021/JP064411Z
Abstract: We report a new application of fluorescence spectroscopy for the identification and characterization of chemical species in complex environments. Simultaneous collection of a dispersed fluorescence spectrum for every step of the laser wavelength results in a two-dimensional spectrum of emission versus excitation wavelengths. This two-dimensional fluorescence (2DF) spectrum yields quick and intuitive assignments of a multitude of peaks in the separate fluorescence excitation and dispersed fluorescence spectra as belonging to the same species. We demonstrate the technique with the measurement of 2DF spectra of a discharge of dilute benzene into a supersonic free jet. A multitude of rovibronic bands due to the C(2) Swan and C(3) comet bands are immediately apparent and even unreported bands can be assigned intuituvely. Custom software filters are employed to enhance or reject emission from one or the other carrier to obtain excitation spectra arising from purely one carrier, or even a specific spectral component of a single carrier. The very characteristic 2DF fingerprints of C(2) and C(3) permit identification of another unidentified species in the discharge that absorbs at 476 nm, coincident with one of the diffuse interstellar bands.
Publisher: AIP Publishing
Date: 13-04-2009
DOI: 10.1063/1.3110682
Abstract: The D1(A2″)−D0(A2″) electronic transition of the resonance-stabilized 1-phenylpropargyl radicalooled discharge of 3-phenyl-1-propyne, has been investigated in detail by laser-induced fluorescence excitation and dispersed single vibronic level fluorescence (SVLF) spectroscopy. The transition is dominated by the origin band at 21 007 cm−1, with weaker Franck–Condon activity observed in a′ fundamentals and even overtones and combinations of a″ symmetry. Ab initio and density functional theory calculations of the D0 and D1 geometries and frequencies were performed to support and guide the experimental assignments throughout. Analysis of SVLF spectra from 16 D1 vibronic levels has led to the assignment of 15 fundamental frequencies in the excited state and 19 fundamental frequencies in the ground state assignments for many more normal modes not probed directly by fluorescence spectroscopy are also suggested. Duschinsky mixing, in which the excited state normal modes are rotated with respect to the ground state modes, is prevalent throughout, in vibrations of both a′ and a″ symmetry.
Publisher: AIP Publishing
Date: 22-02-2007
DOI: 10.1063/1.2484344
Abstract: The jet-cooled laser-induced fluorescence and dispersed fluorescence spectra of the S1(A1′)←S0(A1′) transition of triphenylene are reported. The spectra exhibit false origins of e′ symmetry which are modeled by performing calculations of Herzberg-Teller coupling using time-dependent density functional theory. It is found that this level of theory reproduces the main features of the observed spectra. The oscillator strength of the strongest band is calculated to be f=7×10−4. From a combination of theory and the observed upper state lifetime of 41ns, an estimate of the fluorescence yield is made of ΦF=0.084, in agreement with previous studies in the condensed phase.
Publisher: AIP Publishing
Date: 22-07-2009
DOI: 10.1063/1.3175013
Abstract: A new band system of C2, e Π3g−c Σ3u+ was studied by ab initio quantum chemical and experimental methods. The calculations were carried out at the multireference configuration interaction level of theory with Davidson’s correction using aug-cc-pV6Z basis set and include core and core-valence correlation as well as relativistic corrections computed with aug-cc-pCVQZ and cc-pVQZ bases, respectively. The vibrational energies and rotational constants of the upper e Π3g state were calculated from the computed ab initio potential energy curve. The ab initio results indicate that the electronic transition moment of the e Π3g−c Σ3u+ system is approximately one-half that of the Fox–Herzberg e Π3g−a Π3u system. Franck–Condon factors were calculated for both systems and used to guide experiments aimed at discovering the e Π3g−c Σ3u+ system. The e Π3g(v′=4)−c Σ3u+(v″=3) band of jet-cooled C2 was successfully observed by laser-induced fluorescence spectroscopy by monitoring the ensuing e Π3g−a Π3u emission.
Publisher: American Astronomical Society
Date: 03-2006
DOI: 10.1086/499260
Publisher: American Chemical Society (ACS)
Date: 28-08-2009
DOI: 10.1021/JA904521C
Abstract: The cis-1-vinylpropargyl (cis-1VPR, cis-pent-4-en-1-yn-3-yl) and trans-1-vinylpropargyl (trans-1VPR, trans-pent-4-en-1-yn-3-yl) radicals, produced in a supersonically cooled hydrocarbon discharge, have been identified by a synergy of 2-dimensional fluorescence and ionization spectroscopies, revealing their electronic origin transitions at 21,232 and 21,645 cm(-1) respectively. These assignments are supported by an excellent agreement between calculated ground state frequencies of cis-1VPR and trans-1VPR with those obtained by dispersed fluorescence spectroscopy. In addition, high-resolution rotational contours of the two bands are well simulated using calculated X- and A-state trans-1VPR and cis-1VPR rotational constants. Finally, computed origin transition energies of these two isomers are within several hundred wavenumbers of the observed band positions. With the 1-phenylpropargyl radical, the 1VPR isomers are the second 1-substituted propargyl species to have been observed abundantly from a hydrocarbon discharge, while no 3-substituted analogue has been positively identified. This is likely due to the greater resonance stabilization energy of the 1-substituted species, arising from concerted delocalization of the unpaired electron over the vinyl and propargyl moieties.
Publisher: American Chemical Society (ACS)
Date: 29-01-2018
Abstract: The products of an electrical discharge containing toluene are interrogated using resonance-enhanced multiphoton ionization and laser-induced fluorescence spectroscopies. A previously unreported electronic spectrum recorded at m/z = 105, with a putative origin band at 26053 cm
Publisher: AIP Publishing
Date: 04-12-2007
DOI: 10.1063/1.2805090
Abstract: A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the dΠg3←cΣu+3 and dΠg3←aΠu3 excitations. Rotationally resolved excitation spectra of the (4←1), (5←1), (5←2), and (7←3) bands in the dΠg3←cΣu+3 system of C2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the cΣu+3 state. The principal molecular constants for the cΣu+3 state are Be=1.9319(19)cm−1, αe=0.01855(69)cm−1, ωe=2061.9cm−1, ωexe=14.84cm−1, and T0(c−a)=8662.925(3)cm−1. We report also the first experimental observations of dispersed fluorescence from the dΠg3 state to the cΣu+3 state, namely, dΠg3(v=3)→cΣu+3(v=0,1).
Publisher: AIP Publishing
Date: 10-07-2009
DOI: 10.1063/1.3171934
Publisher: AIP Publishing
Date: 18-05-2006
DOI: 10.1063/1.2196886
Abstract: A high-resolution single vibronic level emission study from the ÃΠ3∕22 state of the HC4S radical is reported. Ground state density functional theory frequencies have been used to assign ground state vibronic levels involving three stretching modes ν2, ν3, and ν5 in the region of 0–3250cm−1, while the frequency of ν4 remains speculative. Tentative assignments are given for the complicated structures arising from Renner-Teller and spin-orbit interactions within the bending energy levels. From analysis of the dispersed emission spectra, Fermi resonances involving pairs of bands have been identified in the ÃΠ3∕22←X̃Π3∕22 laser induced fluorescence spectrum.
Publisher: AIP Publishing
Date: 18-12-2006
DOI: 10.1063/1.2408412
Abstract: A new band system of C2, dΠg3←cΣu+3 is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the cΣu+3 state of C2. Observations were made by laser excitation of cΣu+3(v″=0) C2, produced in an acetylene discharge, to the dΠg3(v′=3) level, followed by detection of Swan band fluorescence. Rotational analysis of this band yielded rotational constants for the cΣu+3(v″=0) state: B0=1.9218(2)cm−1, λ0=−0.335(4)cm−1 and γ0=0.011(2)cm−1. The vibrational band origin was determined to be ν3−0=15861.28cm−1.
Location: United States of America
No related grants have been discovered for Neil Reilly.