High-resolution laser spectroscopy RF02 High-resolution laser spectroscopy of the B ← X transition of 14NO3 radical: Vibrationally excited states of the B state Shunji Kasahara1, Kohei Tada1, Michihiro Hirata1, Takashi Ishiwata2, and Eizi Hirota3 1 Kobe University, Japan; 2 Hiroshima City University, Japan; 3 The Graduate University for Advanced Studies, Japan; 71st International Symposium on Molecular Spectroscopy @ Champaign-Urbana, Illinois, The United States 23rd June 2016

Absorption spectrum of 14NO3 (Visible) 　Introduction NO2 + O3 → NO3 + O2 N2O5 ⇄ NO3 + NO2 B 2E’ ： …(4e’)3 (1e’’)4 (1a2)2 ~ 15000 cm-1 A 2E’’： …(4e’)4 (1e’’)3 (1a2)2 ~ 7000 cm-1 X 2A2’： …(4e’)4 (1e’’)4 (1a2)1 0 cm-1 D3h 2NO2 HNO3 + R etc. NO2　+ O NO　+ O2 + NO + RH NO3 + hν Absorption spectrum of 14NO3 (Visible) J. Chem. Soc. Faraday 1176, 785 (1980). Wavenumber / 1000 cm-1 20 15 10 5 NO2 + O 　　　　NO3 NO + O2 Vibronic Band ~ 16000 cm-1 (~ 625 nm) O2 (b 1Σg+) B 2E’ 0-0 band ~ 15100 cm-1 (~ 662 nm) B – X transition O2 (a 1Δg) A 2E’’ 662 nm O2 (X 3Σg-) X 2A2’ reaction coordinate K. Mikhaylichenko et al., J. Chem. Phys., 105, 6807 (1996)

Photochemistry of NO3 radical: photo-dissociation NO3 is photolyzed to NO2 + O or NO + O2 in ≤ 630 nm (≥ 15900 cm-1) region. Abs. spectrum of NO3 NO3 + hν → NO + O2 → NO2 + O Inter-electronic interaction is important to the photolysis pathways. The vibrationally excited B 2E′ state should be interesting spectroscopically. “bright state”: B 2E′ state “first and second excited states”: (degenerated) A 2E″ state Magnotta, and Johnston, Geophys. Res. Lett. 7(10), 769 (1980). Xiao, Maeda, and Morokuma, J. Chem. Theory Comput. 8, 2600 (2012).

Laser-Induced Fluorescence (LIF) Spectra of NO3 B-X transition Tada, Kashihara, Baba, Ishiwata, Hirota, and Kasahara, J. Chem. Phys. 141, 184307 (2014). 14NO3 15NO3 15000 15500 16000 16500 Wavenumber / cm-1 000 110 420 110 Δ N2O5 → NO3 + NO2 420 000 Tada, Teramoto, Ishiwata, Hirota, and Kasahara, J. Chem. Phys. 142, 114302 (2015). Fukushima and Ishiwata, 67th Int. Symp. Mol. Spectrosc. TI06 (2012). Vibrational assignment by Professor Fukushima (Hiroshima City University)

Summary of 0-0 bands： Assigned line pairs of 14NO3 and 15NO3 0.0247 cm-1 2E′3/2 ← X 2A2′ 2E′1/2 ← X 2A2′ 2E′1/2 ← X 2A2′ Wavenumber / cm-1 2E′3/2 2E′1/2 X 2A2′ (k″ = 0, N″ = 1) J’ = 1.5 J′ = 1.5 J′ = 0.5 J″ = 0.5 J″ = 1.5 Q R P 0.0247 cm-1 14NO3: Tada, et. al., J. Chem. Phys. 141, 184307 (2014) 15NO3: Tada, et. al., J. Chem. Phys. 142, 114302 (2015)

LIF Spectra of NO3 B-X transition Tada, Kashihara, Baba, Ishiwata, Hirota, and Kasahara, J. Chem. Phys. 141, 184307 (2014). 14NO3 15NO3 15000 15500 16000 16500 Wavenumber / cm-1 000 110 420 110 Δ N2O5 → NO3 + NO2 0 + 770 cm-1 band 420 000 15000 15500 16000 16500 Intensity×5 Tada, Teramoto, Ishiwata, Hirota, and Kasahara, J. Chem. Phys. 142, 114302 (2015). 14NO2 R. E. Smalley et al., J. Chem. Phys., 63, 4977 (1975) Fukushima and Ishiwata, 67th Int. Symp. Mol. Spectrosc. TI06 (2012). Vibrational assignment by Professor Fukushima (Hiroshima City University)

Experimental setup I Absolute wavenumber mesurement system (Accuracy : 0.0001 cm-1) Single mode laser ( Γ = 0.00003 cm-1 ) PBS PD BS Nd:YVO4 Laser Ring Dye Laser I2 Cell 532 nm around 660 or 625 nm EOM Etalon D Molecular Beam (Typical linewidth : 0.0007 cm-1) Photon Counter PMT Liq. N2 Filter Pulsed Nozzle N2O5 + Ar Computer NO2 + Ar BS : Beam splitter PBS : Polarization beam splitter EOM : Electro-optic modulator PD : Photo diode PMT : Photomultiplier tube Heater 300 ℃ Heater off Slit (2 mm) Mirror & Magnet N2O5 → NO3 + NO2 Skimmer (ϕ= 2 mm) Pump Pump

LIF spectra of 14NO3 and 14NO2 0 + 770 cm-1 band Resolution：0.2 cm-1 15000　　　 15200　　　 15400　　　 15600　　　 15800　　　 16000　　　 16200　　　 16400 Wavenumber / cm-1 0 + 770 cm-1 band N2O5 → NO3 + NO2 M. Fukushima et al., 67th Int. Symp. Mol. Spectrosc., TI06 (2012) 15000　　　 15200　　　 15400　　　 15600　　　 15800　　　 16000　　　 16200　　　 16400 Wavenumber / cm-1 INTENSITY ×5 NO2 R. E. Smalley et al., J. Chem. Phys., 63, 4977 (1975)

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) 0.3 cm-1 N2O5 → NO3 + NO2 * * NO2 signal Wavenumber / cm-1 R(4) P(4) ∆N(N″) NO2 R(2) P(6) 15884.9 cm-1 band Trot ~ 15K P(8) P(2) P(10) R(0) P(12) P(14) Wavenumber / cm-1 8

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 N2O5 → NO3 + NO2 NO3 signal NO2 Wavenumber / cm-1 9 1

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) Observed spectrum Very complicated Less regularity Wavenumber / cm-1 15890 − 15920 cm-1 (30 cm-1) Assignment Ground State Combination Difference Zeeman splitting pattern これだけではなんとも言えないので、おそらくの物も見せる。 Wavenumber / cm-1

Ground State Combination Difference The matrix elements of X 2A2′ (υ = 0) state of NO3 J 1 3 5 0.5 1.5 2.5 3.5 4.5 5.5 k=0 N Energy / cm-1 10 15 a = b N = J － S c K Hund’s coupling case (b) Molecular constants of NO3 in the X 2A2′ (υ = 0) state J=1.5 J=0.5 N=1 0.0247 cm-1 Kawaguchi et al., Chem. Phys., 231, 193 (1998). Constants (cm-1) B 0.4585485(63) C B/2 DN×105 0.1113(12) DNK×105 -0.2121(27) DK×105 -(2DN+3DNK)/4 εbb -0.01649(13)

Selection rules of B-X transition (perpendicular band) 　 B - X transition: Selection rules Transitions to the 2E′1/2 and the 2E′3/2 Selection rules of B-X transition (perpendicular band) ΔK = ±1, ΔJ = 0, ±1 X 2A2′ (υ″=0, k″=0) J″=0.5 J″=1.5 J′=0.5 J′=1.5 2E′1/2 (k′=1) rR rQ 2E′3/2 (k′=1) rP The nomenclature: ∆k∆J B state: Hund’s coupling case (a) spin−orbit interaction → X state: Hund’s coupling case (b) spin−rotation interaction → These three transitions are detected as two rotational lines with 0.0247 cm-1 spacing. 0.0247 cm-1

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) Transitions from the X 2A2′ (υ = 0, N=1) levels 0.0247 cm-1 spacing line pair Wavenumber / cm-1 15890 − 15920 cm-1 (30 cm-1) 0.3cm-1 固まっているというのは0－0と同じ。だけど、固まった部分が綺麗になっているのではなく、複数ありそうな感じがする。その理由としてはJHもしくは、もともと2つの振電バンドが重なっている事が考えられる。 Wavenumber / cm-1

Unambiguous rotational assignment → Zeeman splitting observation 　High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15918.65 − 15918.95 cm-1 (0.3 cm-1) Rotational lines > 2000 ( 0.001 cm-1 ) FWHM~30 MHz Resolution ≈ 30 MHz (0.001 cm-1) Accuracy of the absolute wavenumber ≈ 3 MHz (0.0001 cm-1) Unambiguous rotational assignment → Zeeman splitting observation 0.0247 cm-1 Wavenumber / cm-1

Experimental setup: Detection of the Zeeman splitting Selection rules for the Zeeman effect H ΔMJ =0 ΔMJ =±1 π-pump (H // E) σ-pump (H⊥E） Photomultiplier tube H: Magnetic field vector, E: Polarization of laser Observed Zeeman splitting at the 0 – 0 band region 0 G 70 G 125 G 190 G 245 G 305 G 360 G H = π-pump σ-pump Electromagnet Fluorescence collecting mirror system Laser beam コイル付近の説明。Zeemanを二種類とれる。今回は全部パイ。 Electromagnet Wavenumber / cm-1

Zeeman Hamiltonians and matrix elements The X 2A2’ state: HZ = gS μB H·S The B 2E’ state: HZ = gS μB H·S + gL μB H·Leff μB (= 4.6686×10-5 cm-1 G-1): Bohr magneton, gS: the electron spin g factor, gL: the electron orbital g factor, and ζed: the effective value of <Λ|Lz|Λ>. Refs: Endo et al., J. Chem. Phys., 81, 122 (1984) Hirota, High-Resolution Spectroscopy of Transient Molecules, Springer (1985) Tada, Kashihara, Baba, Ishiwata, Hirota, and Kasahara, J. Chem. Phys. 141, 184307 (2014)

Unambiguous rotational assignment → Zeeman splitting observation 　High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15918.65 − 15918.95 cm-1 (0.3 cm-1) Rotational lines > 2000 ( 0.001 cm-1 ) FWHM~30 MHz Resolution ≈ 30 MHz (0.001 cm-1) Accuracy of the absolute wavenumber ≈ 3 MHz (0.0001 cm-1) Unambiguous rotational assignment → Zeeman splitting observation 0.0247 cm-1 Wavenumber / cm-1

Zeeman splitting of the B 2E′1/2 - X 2A2′ transitions π-pump (H // E, ΔMJ =0) Observed Zeeman splitting at the 0 − 0 band region π-pump (H // E, ΔMJ =0) 1+2 splitting ΔkΔJk″(J″) rQ0(0.5) rP0(1.5) H=0 G H=0 G 70 G 40 G 125 G 190 G 60 G 245 G 右は0－0で既に帰属の出来ている物。それと同じなので帰属できる。 305 G 85 G 360 G Wavenumber / cm-1 Wavenumber / cm-1

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) Transitions from the X 2A2′ (υ = 0, N=1) levels 0.0247 cm-1 spacing line pair Wavenumber / cm-1 15890 − 15920 cm-1 (30 cm-1) 固まっているというのは0－0と同じ。だけど、固まった部分が綺麗になっているのではなく、複数ありそうな感じがする。その理由としてはJHもしくは、もともと2つの振電バンドが重なっている事が考えられる。 Wavenumber / cm-1

Zeeman splitting of the B 2E′3/2 - X 2A2′ transitions π-pump (H // E, ΔMJ =0) Observed Zeeman splitting at the 0 − 0 band region π-pump (H // E, ΔMJ =0) 2+3 splitting ΔkΔJk″(J″) rQ0(1.5) H=0 G rR0(0.5) H=0 G 60 G 70 G 125 G Wavenumber / cm-1 π-pump (H // E, ΔMJ =0) 190 G 245 G H=0 G 305 G 60 G 360 G Wavenumber / cm-1 Wavenumber / cm-1

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) Transitions to the 2E′3/2 (J′=1.5) Transitions to the 2E′1/2 (J′=0.5) 2E′3/2 2E′1/2 X 2A2′ (k″ = 0, N″ = 1) J’ = 1.5 J′ = 1.5 J′ = 0.5 J″ = 0.5 J″ = 1.5 Q R P 0.0248 cm-1 Wavenumber / cm-1 15890 − 15920 cm-1 (30 cm-1) これだけではなんとも言えないので、おそらくの物も見せる。 Wavenumber / cm-1

High-resolution LIF spectra 14NO3 0 + 770 cm-1 band and 14NO2 15860 − 15890 cm-1 (30 cm-1) Transitions to the 2E′3/2 (J′=1.5) Transitions to the 2E′1/2 (J′=0.5) * * * * * 2E′3/2 2E′1/2 X 2A2′ (k″ = 0, N″ = 1) J’ = 1.5 J′ = 1.5 J′ = 0.5 J″ = 0.5 J″ = 1.5 Q R P 0.0248 cm-1 Wavenumber / cm-1 15890 − 15920 cm-1 (30 cm-1) * * * * * * * 固まっているというのは0－0と同じ。だけど、固まった部分が綺麗になっているのではなく、複数ありそうな感じがする。その理由としてはJHもしくは、もともと2つの振電バンドが重なっている事が考えられる。 * * Wavenumber / cm-1 * Probably : S/N ratio is not enough for the Zeeman measurement

Summary This study: LIF spectrum of the B − X transition 15900 cm-1 band LIF spectrum of the B − X transition We have observed high-resolution fluorescence excitation spectra of 14NO3 B-X transition for the 0+770 cm-1 band [15860 – 15920 cm-1]. Observed rotational line are weak compared with the ones of 0-0 band. In the observed region, more than 3000 rotational lines were found. Rotational assignment is difficult except the transitions from the X 2A2’ (K” = 0, N” = 1) levels. (0.0248 cm-1 pairs) Unambiguous assignment of these 0.0248 cm-1 pairs is completed from the observed Zeeman splittings. The transitions to the 2E’3/2 and 2E1/2 were observed as the several pairs and these pairs make groups. (not random distribution) Resolution: 0.2 cm-1 N2O5 → NO3 + NO2 Pyrolysis: 00 10 1 15000 15500 16000 16500 NO3 + NO2 [1] 40 2 * * NO2 signal * * * * * * Wavenumber / cm-1 ここではどうなっているのか。 Wavenumber / cm-1 Wavenumber / cm-1

Acknowledgement Prof. Masaaki Baba (Kyoto University) for experimental setup at early stage. Ms. Hitomi Matsubara and Mr. Tsuyoshi Takashino (Undergraduate students, Kobe University) for their help. Prof. Masaru Fukushima (Hiroshima City University) for his LIF spectrum of 15NO3. Japan Society for the Promotion of Science for the financial support. Thank you for your attention!

< 2E′3/2 – X 2A2′ transition (0 – 0 band) > 　Zeeman effect around 15872.4 cm-1 2E′3/2 – X 2A2′ transition < 2E′3/2 – X 2A2′ transition (0 – 0 band) > J′ = 1.5 MJ + 1.5 + 0.5 0.5 1.5 - 0.5 J″ = 0.5 J″ = 1.5 0.0246 cm-1 rQ0(1.5) rQ0(1.5) rR0(0.5) rR0(0.5) 0.0243 cm-1 Magnetic field 0.0248 cm-1 0 G 40 G 70 G Tada et al., J. Chem. Phys. 141, 184307 (2014). Wavenumber / cm-1 Wavenumber / cm-1

Vibrational Assignment M. Fukushima et al., 67th Int. Symp. Mol. Spectrosc., TI06 (2012) 0 + 950 cm-1 band 0 - 0 band ν1 15000　　　　　　15400　　　 　　　15800　　　 　　　16200　　　 Wavenumber / cm-1 　　　 E’ 　 ν = E’ a1’, a2’, e’ B state Vibrational level Vibronic level 0 + 770 cm-1 band 2ν4 Normal Mode of NO3 　　　　 + 　　-　　　　 - - 　　　　　　ν2 　　A2” 　　　　　　ν1 　　A1’ 　　　ν3a E’ 　　　ν3b 　　　ν4a 　　　ν4b 振動 モード 既約表現 遷移波数 (cm-1) X[1] [2] A[3] B ν1 a1’ 1060 780 950 ν2 a2” 762 710 ν3 e’ 1480 (?) 1435 ν4 380 530 ~ 385 [1] T. Ishiwata et al., J. Phys. Chem., 87, 1349 (1983) [2] R. R. Friedl et al., J. Phys. Chem., 91, 2721 (1987) [3] T. J. Codd et al., 68th Int. Symp. Mol. Spectrosc., WJ05 (2013)

Complicated structure of the 662 nm band Vib. mode Frequency Anharmonic constant ν1 (a1’) ν2 (a2”) ν3 (e’) ν4 (e’) 772.73 713.59 1688.12 511.20 – 4.603 – 10.268 + 4.785 [Codd et al., 67th OSU meeting, TI01 (2012)] The A state vibrational frequencies in cm-1 { B 2E’ 15100 cm-1 A 2E” 7060 cm-1 E” × A2” = E’ 15070 – 15145 cm-1 region: 10 ~ 15 E’-type levels Complicated structure of the 662 nm band: (mainly) vibronic interaction with dark A state?? X 2A2’