High-Resolution Photoelectron Spectroscopy of CryogenicallyCooled NO3 Mark C. Babin,† Jessalyn A. DeVine,† Martin DeWitt,† John F. Stanton,*,∇

and Daniel M. Neumark*,†,⊥

†Department of Chemistry, University of California, Berkeley, California 94720, United States∇Quantum Theory Project, Department of Chemistry and Physics, University of Florida, Gainesville, Florida 32611, United States⊥Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

*S Supporting Information

ABSTRACT: High-resolution anion photoelectron spectra of cryogenically cooled NO3anions obtained using slow photoelectron velocity-map imaging are presented and providenew insight into the vibronic structure of the corresponding neutral radical. Acombination of improved spectral resolution, measurement of energy-dependent intensityeffects, temperature control, and comparison to theory allows for full assignment of thevibronic features observed in this spectrum. We obtain a refined electron affinity of3.9289(14) eV for NO3. Further, the appearance of Franck−Condon forbidden transitionsfrom vibrationally cold anions to neutral states with excitation along the NO3 ν4 modeconfirms that these features arise from vibronic coupling with the B2E′ excited state ofNO3 and are not hot bands, as has been suggested. Together, the suite of experimentaland simulated results provides clear evidence that the ν3 fundamental of NO3 resides near1050 cm−1, addressing a long-standing controversy surrounding this vibrationalassignment.

The nitrate radical (NO3) was one of the first free radicalsto be observed spectroscopically1 and is one of the most

important radicals in atmospheric chemistry. This speciesserves as the primary oxidizer in the nighttime troposphere,when photolysis by sunlight ceases and its concentration buildsup.2 Under these conditions, NO3 reacts to form HNO3, N2O5,and organic nitrates that are subsequently incorporated intoaerosols, providing the largest source of uncertainty of theconcentration of NOx, O3, and OH in atmospheric models.3,4

This interesting chemistry has motivated numerous experi-ments utilizing Fourier transform infrared spectroscopy(FTIR),5−14 dispersed fluorescence (DF),15−17 diode laserspectroscopy,18,19 matrix isolation spectroscopy,20,21 cavityringdown spectroscopy,22,23 and anion photoelectron spec-troscopy,24 as well as several theoretical studies,25−32 tocharacterize the electronic and vibrational structure of NO3.Despite this extensive body of work, the nitrate radical stillpresents a significant challenge to both theory and experi-ment.11,14,31,33 In this Letter, we address questions recentlyposed in the literature about the vibronic structure of the X2A2′ground state of NO3 using high-resolution photoelectronspectroscopy of cryogenically cooled NO3 and accompanyingtheory.The spectroscopy of NO3 is complicated by the existence of

two excited electronic states (A2E″ and B2E′) that lie roughly 1and 2 eV, respectively, above the ground X2A2′ state, as shownin Figure 1a. These three states exhibit a wealth of vibronicmixing that results from both Jahn−Teller (JT) and pseudo-Jahn−Teller (pJT) couplings.22,24,29 The potential energy

surface for the ground state is known to be quite flat byvirtue of a strong X2A2′/B2E′ pJT interaction, with both theoryand experiment predicting symmetric (D3h) and asymmetric(C2v) structures at various times.25,26,28,34−36 While the D3hstationary point has not been unambiguously demonstrated tobe a minimum or a (second-order) saddle point between

Received: October 17, 2019Accepted: November 25, 2019Published: November 25, 2019

Figure 1. Electronic levels (a) and vibrational modes (b) in NO3 andNO3. The “±” signs signify out-of-plane motion.

Letter

pubs.acs.org/JPCLCite This: J. Phys. Chem. Lett. 2020, 11, 395−400

© XXXX American Chemical Society 395 DOI: 10.1021/acs.jpclett.9b03055J. Phys. Chem. Lett. 2020, 11, 395−400

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equivalent C2v structures, it is clear that the vibrationallyaveraged ground-state structure has D3h symmetry.29

Strong vibronic mixing between the ground X2A2′ state withthe B2E′ excited state was first suggested by Weaver et al.,24

whose photoelectron spectrum of NO3− is presented in Figure

2a. Peak a, located ∼360 cm−1 above the 000 vibrational origin,

was assigned to the Franck−Condon (FC) forbidden 401

transition involving the ν4 degenerate bend of the neutral,which becomes allowed through pJT coupling. More recenttheoretical work has shown that a relatively simple vibronicmodel accounts qualitatively for this behavior as well as anumber of other spectroscopic properties of NO3, such as theX−B absorption spectrum and the DF spectrum in which theground state is accessed from the lowest vibronic level of theB2E′ state.29 This vibronic model also questioned the priorassignment of the strongest infrared absorption of NO3(∼1492 cm−1) to the ν3 degenerate stretch,18 ascribing itinstead to a combination level; the true ν3 position wascalculated to be nearly 500 cm−1 lower. Subsequent and morequantitative work31 predicted that ν3 and the totally symmetricstretch (ν1) fundamentals reside close together (within 10cm−1) and that the former is the main contributor of intensityto the peak found ∼1050 cm−1 above the origin, b, in the NO3photoelectron spectrum (Figure 2a). This implies that peak bmay comprise both the FC-allowed 10

1 and FC-forbidden 301

transitions, contradicting the original assignment to the 101

transition by Weaver et al. The reassignment of the ν3frequency has led to numerous studies of the vibronic levelsand spectra of NO3.

6,9,10,12−14,20,21,23,37,38 Particularly note-worthy is a recent paper by Hirota33 that questions the very

existence of strong X2A2′/B2E′ vibronic coupling, referencingwork by Yamada and Ross39 that claims that peak a in Figure2a was misassigned by Weaver et al. and instead corresponds tothe FC-allowed 41

3 hot band.The present study aims to address both of these critiques of

the Weaver spectral assignments by using slow photoelectronvelocity-map imaging of cryogenically cooled anions (cryo-SEVI)40 to revisit the photodetachment spectrum of NO3.Compared to the experiments of Weaver et al., cryo-SEVIoffers considerably higher resolution, removal of hot bands viacryogenic cooling of anions, and facile evaluation of theelectron kinetic energy (eKE) dependence of peak intensitiesand photoelectron angular distributions (PADs). The lattertwo attributes shed light on the nature of the electronic statesaccessed by photodetachment, demonstrating that the ν4 andν3 fundamentals in the X2A2′ state of NO3 gain intensitythrough vibronic coupling to the B2E′ state. We confirm theinitial assignment set forth by Weaver for peak a as the ν4fundamental and find that b is indeed dominated by theproximate 30

1 band. Excellent agreement between ourexperimental spectra and high-level calculations affirms theseassignments.The cryo-SEVI spectrum of the X2A2′ ← X1A1′ photodetach-

ment transition of NO3 is presented in Figure 2b, where a low-resolution overview spectrum is displayed atop high-resolutioncomposite spectra taken at several photon energies. Inaddition, the cryo-SEVI results are compared to a simulatedphotoelectron stick spectrum, constructed using a three-stateKoppel−Domcke−Cederbaum (KDC) vibronic Hamiltonianfor NO3.

41 Electron binding energies (eBEs) relative to theneutral electron affinity (EA) are given in Table 1 for all

labeled transitions, alongside the KDC-predicted values andpeak assignments. Details of the cryo-SEVI and theoreticalmethods are provided in sections S1 and S2, respectively, ofthe Supporting Information (SI). A complete listing of theeigenvalues of the KDC Hamiltonian and the experimentallydetermined parameters with a comparison to literature valuesare presented in Tables S1 and S2, respectively, of the SI.There are several notable differences between the Weaver

and cryo-SEVI spectra. First, the improvement in resolutionprovides a more precise EA for neutral NO3. This is best

Figure 2. Photoelectron spectra of the X2A2′ ← X1A1′ transition ofNO3 as reported in ref 25 (a) and this work using cryo-SEVI (b). In(b), a low-resolution spectrum (gray, hν = 35137 cm−1) sits aboveboth high-resolution scans (black, variable photon energy) and asimulated photoelectron stick spectrum. Red sticks represent FC-allowed transitions, and blue sticks represent transitions that gainintensity through pJT coupling.

Table 1. Positions, Shifts Relative to the EA Extracted fromPeak G (EA = 31689(11) cm−1), Assignments, andCorresponding KDC Eigenvalues for DetachmentTransitions in the Cryo-SEVI Spectrum of NO3 Presentedin Figure 2b.a

peak eBE (cm−1) eBE−EA (cm−1) assignment KDC

A 31707(25) 000

B 32045(8) 356 401 369

C 32459(14) 770 402 777

D 32733(12) 1044 301 1069

E 32871(14) 1182 403 1152

F 33102(14) 1413 10140

1 1424G 33181(11) 1492 30

1401 1494

H 33256(12) 1567 404 1579

I 33609(12) 1920 30140

2 1931J 33837(11) 2148 30

2 2157aUncertainties in peak positions correspond to one standard deviationobtained from a Gaussian fit to the corresponding feature in the high-resolution scan.

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obtained by fixing the shift from the origin for the narrowestfeature in our spectrum, peak G, to the corresponding valuefrom IR measurements, 1492 cm−1, and subtracting thevibrational frequency from this peak position in eBE. Thisprocedure yields an EA of 3.9289(14) eV, an order ofmagnitude more precise than the value of 3.937(14) eVdetermined by Weaver et al. Another notable difference is theabsence of the 41

1 feature in the cryo-SEVI spectrum. Theabsence of this hot band suggests negligible population ofvibrationally excited anions, as is typical for cryo-SEVIexperiments, where ions usually have internal temperatureson the order of 10 K.40,42 Given the disappearance of the 41

1

hot band but not the disputed 401 feature (B) in the cryo-SEVI

spectrum, we can confidently reject the reassignment of thelatter as the 41

3 hot band.33 Peak B (a in Figure 2a) is indeedthe originally assigned FC-forbidden 40

1 transition, which gainsits activity through vibronic coupling to the B2E′ excited state,in agreement with our simulated photoelectron spectrum.On the basis of the assignment of peak B, we assign C and E

to the 402 and 40

3 transitions. The position of the 403 transition

(Table 1) is consistent with previous infrared measurements inneon matrixes20 and in the gas phase.13 In these works, thevalue of 1173 cm−1 for the e′ sublevel of 3ν4 has beenconfirmed by both isotopic and rotational analyses, respec-tively, leaving no dispute about this assignment to the l=±1vibrational angular momentum sublevels of the NO3 ν4=3state.FC-forbidden features such as B acquire nonzero intensity

through pJT coupling to an excited electronic state withappropriate symmetry.43 Within the (crude) Born−Oppen-heimer approximation, the ν4=1 level of the X2A2′ state andν4=0 level of the B

2E′ state can be written as |a0⟩ = |ν4=1⟩|2A2′⟩

and |b0⟩ = |ν4=0⟩|2E′⟩, respectively; the transition from the

anion ground state |0⟩=|ν=0⟩| 1A1′⟩ to |a0⟩ is FC-forbiddenbecause the ν4 mode is not totally symmetric, whereasphotodetachment to |b0⟩ is FC-allowed. However, states |a0⟩and |b0⟩ each have overall E′ vibronic symmetry and can thusmix by pJT coupling, leading to two new states |a⟩ = c1a|a0⟩ +c1b|b0⟩ and |b⟩ = c2a|a0⟩ + c2b|b0⟩, each of which is an admixtureof the two zero-order vibronic levels. By this vibronic couplingmechanism, the 40

1 transition acquires intensity and can beobserved. A similar mechanism applies to the 40

3 transition (E).The role of vibronic coupling can also be seen in the

dependence of peak intensities and PADs on the eKE.44−46

The spectra in Figure 2 show that the relative intensity of thevibrational origin (A) is much higher in the Weaver spectrumthan in any of the cryo-SEVI spectra, a consequence of thelower photon energies used in the current work. This intensitydependence is explored in greater detail in Figure 3a, in whichthree cryo-SEVI spectra taken at different photon energies andnormalized to the intensity of peak B are shown. Theintegrated intensities of peaks A, B, and D (normalized topeak B) are plotted as a function of eKE for all experimentalspectra in Figure 3b. These data show that at lower eKE theintensity of peak A drops off much more than that of B and D(a and b in the Weaver spectrum). Hence, the near-thresholddetachment cross section of the FC-allowed peak A is verydifferent from that of B, which is allowed only through pJTcoupling. The similar intensity dependence of B and Dsuggests that vibronic coupling is also responsible for asubstantial portion of the intensity of D, as discussed in moredetail below.

The PADs were also determined at multiple photonenergies. The functional form of a PAD is given by47

σ σπ

β θΩ

= [ + ]Pdd 4

1 (cos )tot2 (1)

where σtot is the total detachment cross section, P2(x) is thesecond-order Legendre polynomial, θ is the angle of theoutgoing photoelectron with respect to the laser polarizationaxis, and β is the anisotropy parameter, which ranges from −1(perpendicular detachment) to +2 (parallel detachment).Figure 4 shows β for peaks A, B, and D as a function ofeKE. Clearly, not only the intensity but also the PAD of Aexhibits a markedly different energy dependence than those ofB and D.The pJT coupling mechanism is reflected in the striking

differences in the eKE-dependent intensities and PADs of Aand B. We first consider Figure 3, which shows that as the eKEis lowered, the intensity of the FC-allowed peak (A) issuppressed relative to the vibronically allowed peak (B). Thiseffect arises because photodetachment cross sections at loweKE are governed by the Wigner threshold law48

σ ∝ +(eKE)l 1/2 (2)

where σ is the detachment cross section and l is the angularmomentum of the detached electron. Thus, at low eKE, thelowest-l detachment channels dominate. For detachment to theX2A2′ state of NO3, selection rules for molecular photodetach-ment prohibit detachment of l=0 electrons, and p-wave

Figure 3. (a) Cryo-SEVI spectra of NO3 at three photon energiesillustrating the differing signal attenuation for features A, B, and D aseKE decreases. The intensity of each scan has been normalized to B.Photon energies used are 35137 (black), 33898 (red), and 32801cm−1 (blue). (b) Integrated intensities of features A, B, and D,normalized to B in each scan, for all cryo-SEVI scans, shown in (a).

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detachment dominates.49,50 Hence, the cross section for a FC-allowed transition to the X2A2′ state, such as the 00

0 transition,drops precipitously as the eKE is lowered.In contrast, the 40

1 transition terminates in a neutral levelwith some contribution from the B2E′ electronic state,detachment to which can proceed via l=0 (s-wave) detach-ment. The less severe near-threshold attenuation of s-wavedetachment then yields the observed enhancement in relativeintensity of the 40

1 vs the 000 transition as eKE is lowered. This

situation, in which FC-allowed transitions are suppressed atlow eKE relative to pJT-active features, was seen in the cryo-SEVI spectrum of the indenyl anion,46 though the effect ismuch more pronounced here because the total cross sectionfor detachment to the X2A2′ state is relatively low, as discussedpreviously.24 Hence, a small amount of vibronic mixing withthe B2E′ state markedly affects the intensity of a pJT-activetransition.These effects also govern the eKE-dependent PADs in

Figure 4. Differing PADs in a single photodetachment band area clear signature of vibronic coupling effects.44,51 As the PADreflects the angular momentum of the detached electron,52 thepartial wave components that play a role in eq 2 are intimatelyconnected to the PADs of different detachment transitions,and differences in threshold behavior tend to occur togetherwith different PADs.51,53 This is true in NO3, where the PADfor A is consistent with p-wave detachment, while B displaysthe expected trend for a transition comprising s- and d-wavedetachment. The disparity in the PADs of A and B, coupledwith their threshold behavior, unequivocally shows that B gainsits intensity through pJT coupling.We now consider peak D. Its relative intensity remains high

even at eKEs below 100 cm−1, and its anisotropy parameter βbecomes increasingly negative as the photon energy increases,showing similar behavior to peak B. These two trends suggestthat D gains much of its intensity through the same pJTcoupling mechanism as B and is not solely the FC-allowed 10

1

transition assigned previously. Only two states of e′ symmetry,the appropriate symmetry to pJT-couple to the B2E′ state,plausibly reside near this feature, namely, 3ν4 and the ν3fundamental. As E has been assigned to the 40

3 transition hereand is consistent with the results IR spectroscopy, it can beconcluded that D is then dominated by the 30

1 transition.29

The identification of the pJT-coupled 301 transition in our

spectrum provides the first published experimental evidence,

confirming the theoretical prediction that ν3 lies well below1492 cm−1, and the predicted frequency (1069 cm−1)31 is inreasonable agreement with our experimental value of 1044(16)cm−1. The 10

1 transition cannot be observed directly as itattenuates too rapidly near threshold, where cryo-SEVI mightotherwise achieve sufficient resolution46 to observe thesplitting between the ν1 and ν3 fundamentals.Our findings address recently posed questions regarding the

photoelectron spectrum of NO3−, refute the reassignment of B

as the 413 hot band, and provide the first experimental

confirmation that the ν3 fundamental resides several hundredcm−1 below the 1492 cm−1 band to which it has been assignedand within 10 cm−1 of the ν1 fundamental. Together, theseresults inform an understanding of vital importance regardingvibronic coupling in the X2A2′ ground state of NO3 that shouldlessen the controversy surrounding both the vibrational levelstructure of this radical and the extent that vibronic couplingmanifests in the ground electronic state.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.jpclett.9b03055.

Experimental methods, theoretical methods, and TablesS1 and S2, showing eigenvalues of the Koppel−Domcke−Cederbaum Hamiltonian and experimentalparameters (PDF)

■ AUTHOR INFORMATIONCorresponding Authors*E-mail: johnstanton@ufl.edu.*E-mail: dneumark@berkeley.edu.ORCIDMark C. Babin: 0000-0001-7440-8058Jessalyn A. DeVine: 0000-0003-0091-4286John F. Stanton: 0000-0003-2345-9781Daniel M. Neumark: 0000-0002-3762-9473NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe research conducted at UC Berkeley is funded by the AirForce Office of Scientific Research under Grant No. FA9550-19-1-0051, and the work done at Florida is supported by theDepartment of Energy, Office of Science, Office of BasicEnergy Sciences under Award DE-FG02-07ER15884. M.C.B.thanks the Army Research Office for a National DefenseScience and Engineering Graduate fellowship.

■ REFERENCES(1) Chappuis, J. Etude spectroscopique sur l’ozone. Ann. Sci. EcoleNorm. Sup. 1882, 11, 137−186.(2) Monks, P. S. Gas-phase radical chemistry in the troposphere.Chem. Soc. Rev. 2005, 34, 376−395.(3) Macintyre, H. L.; Evans, M. J. Sensitivity of a global model to theuptake of N2O5 by tropospheric aerosol. Atmos. Chem. Phys. 2010, 10,7409−7414.(4) Brown, S. S.; Stutz, J. Nighttime radical observations andchemistry. Chem. Soc. Rev. 2012, 41, 6405−6447.(5) Kawaguchi, K.; Ishiwata, T.; Tanaka, I.; Hirota, E. Fourier-transform nfrared-spectroscopy of the NO3 radical. Chem. Phys. Lett.1991, 180, 436−440.

Figure 4. Measured anisotropy parameter, β, of the features A, B, andD extracted from spectra obtained at multiple photon energies.

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(6) Ishiwata, T.; Tanaka, I.; Kawaguchi, K.; Hirota, E. High-resolution infrared-spectroscopy of NO3 in the 2500 cm−1 region. J.Mol. Spectrosc. 1992, 153, 167−180.(7) Kawaguchi, K.; Ishiwata, T.; Hirota, E.; Tanaka, I. Infraredspectroscopy of the NO3 radical. Chem. Phys. 1998, 231, 193−198.(8) Kawaguchi, K.; Shimizu, N.; Fujimori, R.; Tang, J.; Ishiwata, T.;Tanaka, I. Fourier transform infrared spectroscopy of the ν3 hot bandof NO3. J. Mol. Spectrosc. 2011, 268, 85−92.(9) Kawaguchi, K.; Fujimori, R.; Tang, J.; Ishiwata, T. FTIRspectroscopy of NO3: perturbation analysis of the ν3+ν4 state. J. Phys.Chem. A 2013, 117, 13732−13742.(10) Fujimori, R.; Shimizu, N.; Tang, J.; Ishiwata, T.; Kawaguchi, K.Fourier transform infrared spectroscopy of the ν2 and ν4 bands ofNO3. J. Mol. Spectrosc. 2013, 283, 10−17.(11) Kawaguchi, K.; Fujimori, R.; Tang, J.; Ishiwata, T. On thevibrational assignment in the ground electronic state of NO3. J. Mol.Spectrosc. 2015, 314, 73−78.(12) Kawaguchi, K.; Narahara, T.; Fujimori, R.; Tang, J.; Ishiwata, T.Infrared spectroscopy of 2ν4 and ν3+2ν4 bands of the NO3 radical. J.Mol. Spectrosc. 2017, 334, 10−21.(13) Kawaguchi, K.; Fujimori, R.; Ishiwata, T. Infrared spectroscopyof the ν1 + ν4 and 3ν4 bands of the nitrate radical. J. Mol. Spectrosc.2018, 347, 56−62.(14) Kawaguchi, K.; Fujimori, R.; Tang, J.; Ishiwata, T. Infraredspectroscopy of the NO3 radical from 2000 to 3000 cm−1. J. Mol.Spectrosc. 2018, 344, 6−16.(15) Nelson, H. H.; Pasternack, L.; Mcdonald, J. R. Laser-inducedexcitation and emission spectra of nitrate radical (NO3). J. Phys.Chem. 1983, 87, 1286.(16) Ishiwata, T.; Fujiwara, I.; Naruge, Y.; Obi, K.; Tanaka, I. Studyof NO3 by Laser-Induced Fluorescence. J. Phys. Chem. 1983, 87,1349−1352.(17) Kim, B. S.; Hunter, P. L.; Johnston, H. S. NO3 Radical Studiedby Laser-Induced Fluorescence. J. Chem. Phys. 1992, 96, 4057−4067.(18) Ishiwata, T.; Tanaka, I.; Kawaguchi, K.; Hirota, E. Infrareddiode laser spectroscopy of the NO3 ν3 band. J. Chem. Phys. 1985, 82,2196−2205.(19) Hirota, E.; Ishiwata, T.; Kawaguchi, K.; Fujitake, M.; Ohashi,N.; Tanaka, I. Near-infrared band of the nitrate radical NO3 observedby diode laser spectroscopy. J. Chem. Phys. 1997, 107, 2829−2838.(20) Jacox, M. E.; Thompson, W. E. The infrared spectroscopy andphotochemistry of NO3 trapped in solid neon. J. Chem. Phys. 2008,129, 204306.(21) Jacox, M. E.; Thompson, W. E. A2E”-X2A2’ transition of NO3

trapped in solid neon. J. Phys. Chem. A 2010, 114, 4712−4718.(22) Okumura, M.; Stanton, J. F.; Deev, A.; Sommar, J. New insightsinto the Jahn-Teller effect in NO3 via the dark A2E “ state. Phys. Scr.2006, 73, C64−C70.(23) Codd, T.; Chen, M. W.; Roudjane, M.; Stanton, J. F.; Miller, T.A. Jet cooled cavity ringdown spectroscopy of the A2E “ ← X2A2’transition of the NO3 radical. J. Chem. Phys. 2015, 142, 184305.(24) Weaver, A.; Arnold, D. W.; Bradforth, S. E.; Neumark, D. M.Examination of the 2A2’ and 2E” states of NO3 by ultravioletphotoelectron spectroscopy of NO3. J. Chem. Phys. 1991, 94, 1740−1751.(25) Davy, R. D.; Schaefer, H. F. Is there an absence of threefoldsymmetry at the equilibrium geometry of the ground electronic statefor NO3. J. Chem. Phys. 1989, 91, 4410−4411.(26) Kaldor, U. The ground-state geometry of the NO3 radical.Chem. Phys. Lett. 1990, 166, 599−601.(27) Mayer, M.; Cederbaum, L. S.; Koppel, H. Ground-statedynamics of NO3 - multimode vibronic borrowing including thermaleffects. J. Chem. Phys. 1994, 100, 899−911.(28) Eisfeld, W.; Morokuma, K. Ab initio investigation of the verticaland adiabatic excitation spectrum of NO3. J. Chem. Phys. 2001, 114,9430−9440.(29) Stanton, J. F. On the vibronic level structure in the NO3 radical.I. The ground electronic state. J. Chem. Phys. 2007, 126, 134309.

(30) Faraji, S.; Koppel, H.; Eisfeld, W.; Mahapatra, S. Towards ahigher-order description of Jahn-Teller coupling effects in molecularspectroscopy: The A2E” state of NO3. Chem. Phys. 2008, 347, 110−119.(31) Simmons, C. S.; Ichino, T.; Stanton, J. F. The ν3 fundamental inNO3 has been seen near 1060 cm−1, albeit some time ago. J. Phys.Chem. Lett. 2012, 3, 1946−1950.(32) Mukherjee, B.; Mukherjee, S.; Sardar, S.; Shamasundar, K. R.;Adhikari, S. A beyond Born-Oppenheimer treatment of five statemolecular system NO3 and the photodetachment spectra of its anion.Chem. Phys. 2018, 515, 350−359.(33) Hirota, E. Assignment of the photoelectron spectrum of thenitrate anion NO3 and vibronic interactions in the nitrate free radical.J. Mol. Spectrosc. 2018, 343, 81−84.(34) Kim, B.; Hammond, B. L.; Lester, W. A.; Johnston, H. S. Abinitio study of the vibrational-spectra of NO3. Chem. Phys. Lett. 1990,168, 131−134.(35) Stanton, J. F.; Gauss, J.; Bartlett, R. J. Potential nonrigidity ofthe NO3 radical. J. Chem. Phys. 1991, 94, 4084−4087.(36) Stanton, J. F.; Gauss, J.; Bartlett, R. J. On the choice of orbitalsfor symmetry-breaking problems with application to NO3. J. Chem.Phys. 1992, 97, 5554−5559.(37) Beckers, H.; Willner, H.; Jacox, M. E. Conflicting observationsresolved by a far IR and UV/Vis study of the NO3 radical.ChemPhysChem 2009, 10, 706−710.(38) Ishiwata, T.; Nakano, Y.; Kawaguchi, K.; Hirota, E.; Tanaka, I.Analyses of the infrared absorption bands of 15NO3 in the 1850−3150cm−1 region. J. Phys. Chem. A 2010, 114, 980−986.(39) Yamada, K.; Ross, S.96th Ann. Meeting Chem. Soc. Jpn.,Kyotanabe, Kyoto, Japan, 2016, Paper 2E6-28.(40) Hock, C.; Kim, J. B.; Weichman, M. L.; Yacovitch, T. I.;Neumark, D. M. Slow photoelectron velocity-map imaging spectros-copy of cold negative ions. J. Chem. Phys. 2012, 137, 244201.(41) Kouppel, H.; Domcke, W.; Cederbaum, L. S. Multimodemolecular-dynamics beyond the born-oppenheimer approximation.Adv. Chem. Phys. 2007, 57, 59−246.(42) Kim, J. B.; Hock, C.; Yacovitch, T. I.; Neumark, D. M. Slowphotoelectron velocity-map imaging spectroscopy of cold thiozonide(S3). J. Phys. Chem. A 2013, 117, 8126−8131.(43) Herzberg, G. Molecular spectra and molecular structure: III.Electronic spectra and electronic structure of polyatomic molecules; VanNostrand Reinhold Company: Princeton, NJ, 1966.(44) Ervin, K. M.; Lineberger, W. C. Photoelectron spectra of C2and C2H. J. Phys. Chem. 1991, 95, 1167−1177.(45) Asmis, K. R.; Taylor, T. R.; Neumark, D. M. Anionphotoelectron spectroscopy of B2N. J. Chem. Phys. 1999, 111,8838−8851.(46) Kim, J. B.; Weichman, M. L.; Yacovitch, T. I.; Shih, C.;Neumark, D. M. Slow photoelectron velocity-map imaging spectros-copy of the C9H7 (indenyl) and C13H9 (fluorenyl) anions. J. Chem.Phys. 2013, 139, 104301.(47) Cooper, J.; Zare, R. N. Angular distribution of photoelectrons.J. Chem. Phys. 1968, 48, 942−943.(48) Wigner, E. P. On the behavior of cross sections near thresholds.Phys. Rev. 1948, 73, 1002−1009.(49) Reed, K. J.; Zimmerman, A. H.; Andersen, H. C.; Brauman, J. I.Cross-sections for photodetachment of electrons from negative-ionsnear threshold. J. Chem. Phys. 1976, 64, 1368−1375.(50) Signorell, R.; Merkt, F. General symmetry selection rules for thephotoionization of polyatomic molecules. Mol. Phys. 1997, 92, 793−804.(51) DeVine, J. A.; Abou Taka, A.; Babin, M. C.; Weichman, M. L.;Hratchian, H. P.; Neumark, D. M. High-resolution photoelectronspectroscopy of TiO3H2: Probing the TiO2 + H2O dissociativeadduct. J. Chem. Phys. 2018, 148, 222810.(52) Sanov, A. Laboratory-frame photoelectron angular distributionsin anion photodetachment: insight into electronic structure andintermolecular interactions. Annu. Rev. Phys. Chem. 2014, 65, 341−363.

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DOI: 10.1021/acs.jpclett.9b03055J. Phys. Chem. Lett. 2020, 11, 395−400

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(53) Babin, M. C.; DeVine, J. A.; Weichman, M. L.; Neumark, D. M.Slow photoelectron velocity-map imaging of cold C7 and C9. J. Chem.Phys. 2018, 149, 174306.

The Journal of Physical Chemistry Letters Letter

DOI: 10.1021/acs.jpclett.9b03055J. Phys. Chem. Lett. 2020, 11, 395−400

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