Communication: Theoretical prediction of the structure and spectroscopic properties of the $\tilde{\mathrm{X}}$X̃ and $\tilde{\mathrm{A}}$Ã states of hydroxymethyl peroxy (HOCH2OO) radical

Delcey, Mickaël G.; Lindh, Roland; Linguerri, Roberto; Hochlaf, M.; Francisco, Joseph S.

doi:10.1063/1.4775782

Cited by 5 publications

(3 citation statements)

References 34 publications

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“…Prior experimental investigations of the ground-state vibrational transitions -either in the gas phase [11,17,18] or within an inert matrix [19,20] -have aided in these assignments. Theoretical work has also helped to disentangle the complex spectra of the ground and first excited states [8,[21][22][23][24][25][26][27][28][29][30][31][32][33], but relatively few high-level ab initio studies are available; many have been limited to HO 2 [3,19,[34][35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 98%

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

2015

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Peroxy radicals (RO 2 ) are intermediates in fuel combustion, where they engage in efficiency-limiting autoignition reactions. They also participate in atmospheric chemistry leading to the formation of unwanted tropospheric ozone. Advances in spectroscopic techniques have allowed for the possibility of employing the lowest (Ã ←X) electronic transition of RO 2 as a tool to selectively monitor these species, enabling accurate kinetic values to be obtained. Herein, high-level ab initio methods are employed to systematically refine spectroscopic predictions for the methyl peroxy radical (CH 3 O 2 ), one of the most abundant peroxy radicals in the atmosphere. In particular, vibrationally corrected geometries and anharmonic vibrational frequencies for both the ground (X 2 A ) and first excited (Ã 2 A ) state are predicted using coupled-cluster theory with up to perturbative triples [CCSD(T)] and large atomic natural orbital basis sets. Equation-of-motion coupled-cluster theory is utilised to compute verticalÃ 2 A ←X 2 A transition properties; a radiative lifetime of 4.7 ms is suggested for the excited state. Finally, we predict the adiabatic excitation energy (T 0 ) via systematic extrapolation to the complete basis limit of coupled-cluster with up to full quadruples (CCSDTQ). After accounting for several approximations, and including an anharmonic zero-point vibrational energy correction, we match experiment for this transition to within 9 cm −1 .

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Section: Introductionmentioning

confidence: 98%

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

2015

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“…Very recently, calculation on the structure and the spectroscopy of the peroxy radicals have been performed by Delcey et al. . Formation of the hydroxy‐methyl radical from HO 2 + CH 2 O has been verified by direct detection of the vibrational and electronic spectra using infrared and near‐infrared cavity Ringdown spectroscopy , though no kinetics of the reaction was reported.…”

Section: Introductionmentioning

confidence: 99%

Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals

Morajkar

Schoemaecker

Okumura

et al. 2013

Int J of Chemical Kinetics

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Rate and equilibrium constants for the reaction of HO2 with formaldehyde trueright130.79993pt CH 2normalO+ HO 2↔ HO CH 2O22.em2.em2.em2.em2.em2.em1em(normalR1) and acetaldehyde trueright118.79993pt CH 3 CHO + HO 2↔ CH 3 CH ( OH )O22.em2.em2.em2.em1em2.em(normalR2) have been directly measured. The concentration of HO2 radicals was followed in a time‐resolved method by coupling cw‐CRDS (cavity ringdown spectroscopy) to laser photolysis. The reaction of HO2 with CH2O (R1) was measured at 50 Torr helium over the temperature range 292–306 K, whereas the reaction of CH3CHO with HO2 (R2) was measured in 50 Torr He but at only 294 K. The observed HO2 decay profiles were modeled to take into account secondary chemistry, especially that of the reaction products, hydroxyl‐peroxy radical adducts. The rate constants for forward and back reactions of (R1) at 297 K were found to be k1 = (3.3 ± 0.6) × 10−14 cm3 molecule−1 s−1 and k−1 = (55 ± 5) s−1, respectively, both roughly a factor of two slower than earlier measurements (possibly due to falloff effects), while the equilibrium constant was found to be K1 = (6.0 ± 1.8) × 10−16 molecule−1 cm3 at 297 K, in good agreement with earlier, more indirect determinations. The equilibrium constant of the reaction with CH3CHO was found to be K2 = (1.7 ± 0.5) × 10−17 molecule−1 cm3 at 294 K, with the forward rate constant k2 = (1.5 ± 0.75) × 10−14 cm3 molecule−1 s−1 and the rate constant for the back reaction k−2 = (900 ± 450) s−1.

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“…After the submission of this manuscript, Delcey et al reported high-level calculations of both the X̃ and Ã states of HMP, computed at the CASPT2 and RCCSD(T) levels of theory. The more accurate RCCSD(T) calculations provide values for the adiabatic transition energy of T 0 = 7360 cm –1 , in excellent agreement with those observed here.…”

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confidence: 99%

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

et al. 2013

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We report vibrational and electronic spectra of the hydroxy-methylperoxy radical (HOCH 2 OO • or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO 2• , and formaldehyde, HCHO. The ν 1 vibrational (OH stretch) spectrum and the A ̃← X ̃electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO 2• . Free radical reactions were initiated by pulsed laser photolysis (PLP) of Cl 2 in the presence of HCHO and O 2 in a flow reactor at 300−330 Torr and 295 K. IR-CRDS spectra were measured in mid-IR and near-IR regions over the ranges 3525−3700 cm −1 (ν 1 ) and 7250−7800 cm −1 (A ̃← X ) respectively, at a delay time 100 μs after photolysis. The ν 1 spectrum had an origin at 3622 cm −1 and exhibited partially resolved P-and R-branch contours and a small Q-branch. At these short delay times, spectral interference from HOOH and HCOOH was minimal and could be subtracted. From B3LYP/6-31+G(d,p) calculations, we found that the anharmonic vibrational frequency and band contour predicted for the lowest energy conformer, HMP-A, were in good agreement with the observed spectrum. In the near-IR, we observed four well spaced vibronic bands, each with partially resolved rotational contours. We assigned the apparent origin of the A ̃← X ̃electronic spectrum of HMP at 7389 cm −1 and two bands to the blue to a progression in ν 15 ′, the lowest torsional mode of the A ̃state (ν 15 ′ = 171 cm −1 ). The band furthest to the red was assigned as a hot band in ν 15 ″, leading to a ground state torsional frequency of (ν 15 ″ = 122 cm −1 ). We simulated the spectrum using second order vibrational perturbation theory (VPT2) with B3LYP/6-31+G(d,p) calculations at the minimum energy geometries of the HMP-A conformer on the X ̃and A ̃states. The predictions of the electronic origin frequency, torsional frequencies, anharmonicities, and rotational band contours matched the observed spectrum. We investigated the torsional modes more explicitly by computing potential energy surfaces of HMP as a function of the two dihedral angles τ HOCO and τ OOCO . Wave functions and energy levels were calculated on the basis of this potential surface; these results were used to calculate the Franck−Condon factors, which reproduced the vibronic band intensities in the observed electronic spectrum. The transitions that we observed all involved states with wave functions localized on the minimum energy conformer, HMP-A. Our calculations indicated that the observed near-IR spectrum was that of the lowest energy X ̃state conformer HMP-A, but that this conformer is not the lowest energy conformer in the A ̃state, which remains unobserved. We estimated that the energy of this lowest conformer (HMP-B) of the A ̃state is E 0 (A , HMP-B) ≈ 7200 cm −1 , on the basis of the energy difference E 0 (HMP-B) − E 0 (HMP-A) on the A ̃state computed at the B3LYP/6-31+G(d,p) level.

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Communication: Theoretical prediction of the structure and spectroscopic properties of the $\tilde{\mathrm{X}}$X̃ and $\tilde{\mathrm{A}}$Ã states of hydroxymethyl peroxy (HOCH2OO) radical

Cited by 5 publications

References 34 publications

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

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Communication: Theoretical prediction of the structure and spectroscopic properties of the $\tilde{\mathrm{X}}$X̃ and $\tilde{\mathrm{A}}$Ã states of hydroxymethyl peroxy (HOCH2OO) radical

Cited by 5 publications

References 34 publications

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

Examining the ground and first excited states of methyl peroxy radical with high-level coupled-cluster theory

Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO2 Radicals

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

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Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals