Feb High-resolution Fourier transform emission spectroscopic study of the molecular ions Yoshihiro Nakashima

Contents 1. General introduction 2. B 2  + – X 2  + transition of the PN + ion 3. A 2  – X 2  transition of the OCS + ion 4. A 2  + – X 2  transition of the BrCN + ion

General introduction 1. General introduction 2. B 2  + – X 2  + transition of the PN + ion 3. A 2  – X 2  transition of the OCS + ion 4. A 2  + – X 2  transition of the BrCN + ion Chapter 1

Molecular ion (cationic species) Terrestrial and extraterrestrial environments flame plasma planetary atmosphere comet interstellar space etc…. Protonated ion molecule + proton (H + ) closed shell ex) H 3 O +, NH 4 +, H 3 + … Radical ion ionization of molecule open shell ex) N 2 +, CO 2 +, HCCH + … Spectroscopic study Ion - molecule reaction

Spectroscopic study of the radical ion Photoelectron spectroscopy Laser spectroscopy MPI or REMPI + LIF or photodissociation Cavity ringdown etc… Matrix isolation spectroscopy present study Fourier transform spectrosocpy (FT) Flowing afterglow technique Electronic energy of ion High-sensitive detection

x M1M1 M2M2 B.S. S D Fourier transform spectrosocpy (FTS) Interferogram F(x) F(x)F(x) Spectrum B( ) FT Michelson interferometer x : path difference : wavenumber

Fourier transform spectrosocpy (FTS) High-resolution spectroscopy ( depend on x ) Determination of accurate frequency Wide spectral range ( 10 – 45,000 cm -1 for Brucker IFS120HR ) Low signal to noise ratio Production method of transient species with high concentration and low noise… Flowing afterglow technique

Flowing afterglow Electronic energy level of He He ( 2 1 S ) : eV,  = 19.7 ms eV,  = 19.7 ms He ( 2 3 S ) : eV,  ～ 150 min eV,  ～ 150 min 1eV = kJ/mol D e (N 2 ) = 946 kJ/mol 1 1 S 2 1 S 2 1 P 3 1 S 3 1 P 2 3 S 2 3 P 3 3 S 3 3 P eV HeI metastable The reaction of molecule with metastable

Flowing afterglow Penning ionization He ( 1 1 S )He* ( 2 3 S or 2 1 S) He ( 1 1 S ) He* ( 2 3 S or 2 1 S) He*M*He ( 1 1 S ) He* + M M* + He ( 1 1 S ) M*( M + )*e - M* ( M + )* + e - ( M + )* M + + h ( M + )* M + + h He* + M ( M + )* + He + e - Penning ionization optical spectroscopy ( PIOS ) 1. low noise 2. stable emission 3. selective production of the ion

A 2  – X 2  transition of OCS + 1. General introduction 2. B 2  + – X 2  + transition of the PN + ion 3. A 2  – X 2  transition of the OCS + ion 4. A 2  + – X 2  transition of the BrCN + ion Chapter 3

Introduction R(OC  S) eV X 2X 2 A 2A 2 B 2+B 2+ 44 v = 0 M. J. Hubin-Frank et al. ( MCSCF-CI ) Isovalent with CO 2 + and CS 2 + Predissociation in A 2  1. repulsive 4   2. Internal conversion from A 2  to X 2  Spectroscopic study is few!

Previous works Oschner et al. 1. Oschner et al. (000)  (000) band LIF spectra of the (000)  (000) band  2  3/2  X 2   of the  2  3/2  X 2    transition. Weinkauf and Boesl 3. Weinkauf and Boesl Photodissociation spectra of the (000)  (000) band (000)  (000) band of the  2  1/2  X 2  1/2  2  1/2  X 2  1/2  transition. 4. C. L. Lugez et al. Infrared absorption Infrared absorption spectrum in Ne matrix. 2. Kakoschke et al. Photodissociation spectra of the A 2   X 2  B 2  +  X 2  A 2   X 2  and  B 2  +  X 2   transitions. A 2  X 2  B 2  + 39,180 31,400 0 cm -1  =3/2  =1/2  =3/2  =1/2

Experimental He (2.5 Torr) OCS (2-3 mTorr) resolution : 0.03 cm -1 spectral region : 20,000 – 28,000 cm -1 accumulation time : 60 hrs. Penning ionization He*(2 3 S) + OCS OCS + + He(1 1 S) (I.P.=11.19 eV)

Observed spectrum cm -1 He S+S+ CO + (2,1)CO + (1,0)CO + (2,0) CO + (3,0)CO + (4,0) He OCS +

A 2  – X 2  transition of OCS + (000)-(002)(000)-(003) (000)-(004)(000)-(005) 3 (CO str.) progression 3 (CO str.) progression cm -1

A 2    – X 2    transition P (J’’) R (J’’) FWHM : 0.05 cm -1 T rot : 300 K

A 2    – X 2    transition Q J’’= P J’’= R R R (1.5) and P(2.5) Weak Q branch A 2   – X 2   transition

A 2    – X 2    transition P (J’’) R (J’’) FWHM : 0.05 cm -1 T rot : 300 K

A 2    – X 2    transition  parity + parityJ’’=23.5J’’=26.5  –type doubling A 2   – X 2   transition P-branch

state constant  =3/2  =1/2 A 2  T (25) (99) B (12) (29) 10 7 D (24) p/2 +q  (11) X 2   (80) (30) x (66) y 333  (18)  z (16) B (13) (28) 10 7 D (32) 0.561(21) 10 3  (20) (51) 10 8  (53)  (33) p/2 +q  (10)     Molecular constants (unit : cm -1 )

Discussion parameter X 2  A 2  X 1  +  1 (CS str.) present study  previous study ab initio  3 (CO str.) present study   previous study ab initio Harmonic frequency  1 (CS str.) :  1 = ( 4B e 3 /D e ) 1/2  3 (CO str.) : (  3 3/2 +  3 1/2 )  2

Rotational constants  =3/2  =1/2 Oschner et al Weinkauf and Boesl B 000 = B 000 (1 + B 000 /A) 3/2 B 000 = B 000 (1  B 000 /A) 1/2 B 000 (X) = (15) cm -1 B 000 (A) = (16) cm -1 B 00v = B 000   3 v +  33 v 2 

Spin-orbit interaction constants X 2X 2 A 2A 2 2   2   2   2   B 000 = B 000 (1 + B 000 /A) 3/2 B 000 = B 000 (1  B 000 /A) 1/2 |T 000 – T 000 | = |A’ – A’’| 1/23/2 A (X) =  380.9(66) cm -1 A (A) =  122.2(66) cm -1   (A’ =  111.8) (A’’ =  367.2)

Bond length of OCS + parameter X 2  A 2  X 1  + r CO (A) present study  previous study ab initio a r CS (A) present study  previous study ab initio a a : K. Takeshita et al. (MRSD-CI) (8  ) 2 (9  ) 2 (2  ) 4 (3  ) 3 : X 2  (8  ) 2 (9  ) 2 (2  ) 3 (3  ) 4 : A 2  3  : S 3p (non-bonding) 2  : CO  (bonding)

Summary 1. Ultraviolet emission spectrum of the A 2  - X 2  transition of the OCS + ion was observed by FT spectroscopy. 2. Rotational analysis of the seven bands, A 2  3/2 (000) - X 2   (00v) ( v=0, 2-5 ) and A 2   (000) - X 2   (00v) ( v=3 and 4 ) transitions, were performed to determine the molecular constants. 3. Spin-orbit interaction constants A and the harmonic frequencies  1 and  3 of A 2  and X 2  were determined. 4. The geometrical difference between X 2  and A 2  was indicated, which was explained by the electronic configuration.

A 2  + – X 2  transition of BrCN + 1. General introduction 2. B 2  + – X 2  + transition of the PN + ion 3. A 2  – X 2  transition of the OCS + ion 4. A 2  + – X 2  transition of the BrCN + ion Chapter 4

BrCN + ion Renner-Teller effect Splitting of the vibronic state by the excitation of the bending vibration X 2  Electronic ground state : X 2  spin-orbit interaction Introduction Vibronic interaction

V + = a ( 1 +  ) (  r) 2 + … V - = a ( 1 –  ) (  r) 2 + … |  |<1|  |>1 NCO, N 2 O + ( X 2  ) NH 2 ( X 2 B 1, A 2  )  : Renner parameter Bending potential function

Large spin-orbit interaction A =  1477 cm cm -1 Introduction spin-orbit interaction Influence of the spin-orbit interaction Renner-Teller effect on the Renner-Teller effect  2 = (20) cm cm -1

Previous works 2. M. A. Hanratty et al. B 2  3/2  X 2  3/2 LIF spectra of the B 2  3/2  X 2  3/2 transition 4. C. Salud et al. Infrared diode laser spectroscopy 1 (CN str.) fundamental band of the 1 (CN str.) fundamental band X 2  3/2 of the X 2  3/2  state 1. J.Fulara et al. Low-resolution emission spectra B 2  3/2  X 2  3/2 of the B 2  3/2  X 2  3/2 and A 2    X 2  A 2    X 2  transitions A 2  + X 2   B 2   0 13,700 19,230 cm -1 (001) (002) (012) (100) 3. M. Rosslein et al. LIF spectra of the B 2  3/2  X 2  3/2 transition to determine the r s -structure r s -structure of BrCN +

Experimental He (1.0 Torr) BrCN (2-3 mTorr) resolution : 0.02 cm -1 spectral region : 11,500 – 15,000 cm -1 accumulation time : 40 hrs. Penning ionization He*(2 3 S) + BrCN BrCN + + He(1 1 S) (I.P.=12.08 eV)

Observed spectrum ( A 2  + - X 2   ) (010)-(000) (010)-(010) (000)-(000) (001)-(011) (000)-(010) (010)-(001) (100)-(100) (001)-(001) (000)-(100)  =3/2  =1/2 (000)-(000) (010)-(010) (001)-(001) (000)-(010)

A 2  + (000) - X 2  3/2 (000) transition P1P1 R 21 P 21 + Q 1 R 1 + Q 21

A 2  + (000) - X 2  3/2 (000) transition P 1 branch 79 BrCN + J’’=35.5J’’= BrCN + J’’=35.5J’’=39.5

A 2  + (000) - X 2  1/2 (000) transition P 2 + Q 12 R 12 + Q 2 P 12 R2R2

Molecular constants (unit : cm -1 ) state constant FT + D.L. D.L. LIF A 2  + 3/ (13) B (51) 10 7 D 0.346(16)  (37) X 2   B 3/ (47) (41) (47) 10 7 D 0.307(15) 0.158(23) 0.86(28) state constant FT + D.L. D.L. LIF A 2  + 3/ (13) B (50) 10 7 D 0.299(16)  (37) X 2   B 3/ (47) (11) (86) 10 7 D 0.262(14) 0.147(60) 1.5(56) 79 BrCN + 81 BrCN + eff A 2  + (000) – X 2  3/2 (000) transition

Molecular constants (unit : cm -1 ) state constant 79 BrCN + 81 BrCN + A 2  + 1/ (46) (59) B a a 10 7 D a a  a  a X 2   B 1/ (62) (67) 10 7 D 0.347(11) 0.214(16) p/2 + q (11) (15) eff 79 B 000 = (32) cm B 000 = (41) cm -1 Rotational constant B 000 B 3/2 = B 000 ( 1 + B 000 /A ) B 1/2 = B 000 ( 1  B 000 /A ) eff A 2  + (000) – X 2  1/2 (000) transition

Spin-orbit interaction constant A = 1/2 – 3/2 79 A =  (48) cm A =  (60) cm -1 X 2  (000) A 2  + (000) X 2   X 2   3/2 1/2 A low resolution emission spectroscopy A =  1477 cm -1

r 0 -structure I =  m k z k 2 0 =  m k z k  I = z Br 2  m Br  m k  m Br +  m k BrCN × z Br zCzC zNzN G species electronic state r BrC r CN BrCN X 1  BrCN + X 2  1.788(54) 1.103(78) 1.745(7) 1.195(8) A 2  (61) 1.064(90) unit : A

A 2  + -  2  transition P2P2 R2R2 P 12 R 12

A 2  + -  2  transition P1P1 R1R1 P 21 R 21

Molecular constants (unit : cm -1 ) state constant 79 BrCN + 81 BrCN + A 2  +  (12) (17) B a a 10 7 D a a  a  a  2  B  (19) (26) 10 7 D (60) (79) p  (27)  (32) A 2  + -  2  state constant 79 BrCN + 81 BrCN + A 2  +  (21) (25) B a a 10 7 D a a  a  a  2  B  (25) (28) 10 7 D (58) (66) p  (46)  (52) A 2  + -  2 

A 2  + (000) X 2  (010)  2 2  2 2 2r2r Discussion Rotational constants B B 010 = (23) cm B 010 = (25) cm -1 B  = B 010  [ (B 010 –  /2) cos 2  ] 2 /2r B  = B 010  [ (B 010 –  /2) cos 2  ] 2 /2r  : spin-rotation interaction constant Parameter r 2r = [ A eff 2 + 4(  2 ) 2 ] 1/2 =  -  2 79 r = (24) cm r = (30) cm -1  

Renner parameter p = 2B 010 sin 2  p = 2B 010 sin 2  = 4B 010  2 /2r = 4B 010  2 /2r state constant 79 BrCN + 81 BrCN +  2  p  (27)  (32)  2  p  (46)  (52) B (23) (25) 2r (24) (30)  (20) 79  =  (27) 81  =  (32)  : Renner parameter p :  –  type doubling constant p :  –  type doubling constant BO 2 (X 2  )  =  0.19 CO 2 + (X 2  u )  =  0.190

Wave fuctions of  2  and  2  Wave fuctions of  2  and  2  sin 2  =  2 /2cos 2  = A eff /2 sin 2  : cos 2  = : Large spin-orbit interaction !

Summary 1. Near-infrared emission spectrum of the A 2  + - X 2  transition of the BrCN + ion was observed by FT spectroscopy. 2. Rotational analysis of the four bands, A 2  + (000) - X 2   (000) (  =3/2 and 1/2 ) A 2  + (000) -  2  and A 2  + (000) -  2 , was performed to determine the molecular constants. 3. The r 0 -structures of BrCN + were obtained and geometrical difference between BrCN and BrCN + was small. 4. Renner parameter was determined to be  =  0.185, and the influence of the Renner-Teller effect on X 2  was turned out to be small due to the large spin-orbit interaction.

Conclusion 2. Electronic transitions of linear triatomic radical cations were observed by FT spectroscopy. 1. Fourier Transform spectroscopy was combined with flowing afterglow technique to detect the polyatomic radical cation. 3. Accurate molecular constants were determined by the analysis of the observed vibronic bands. 5. The analysis of the Renner-Teller effect was accomplished. 4. Bond lengths and the harmonic frequencies of the ions were derived from the molecular constants.

Future works 3. Vibrational transition of the ionic or radical species 1. Detection of the radical species ArF excimer laser (193 nm) = 6.42 eV N 2 *( A 3  + ) = 6.22 eV,  =1.36 sec. Fe(CO) 5 + h (193 nm) FeCO 2. Detection of the triplet state of the molecule Hg* ( 3 P ) = 5.46 eV HCCH + Hg* ( 3 P ) HCCH* + Hg ( 1 S ) Emission or absorption spectrum of the transient species

B 2  + – X 2  + transition of PN + 1. General introduction 2. B 2  + – X 2  + transition of the PN + ion 3. A 2  – X 2  transition of the OCS + ion 4. A 2  + – X 2  transition of the BrCN + ion Chapter 2

Introduction PN + ion Isovalent with N 2 + and P 2 + Shallow well of the potential energy curve in B 2  + Interstellar species r V 3 2   + B 2  + C 2  + Avoided crossing ?

A 2  X 2  + B 2  eV Previous works Obase et al. low-resolution emission spectrum of the B 2  + - X 2  + transition Ahmad and Hamilton medium-resolution emission spectrum of the B 2  + - X 2  + transition Imajo et al. high-resolution FT emission spectrum of the B 2  + (v=0) - X 2  + (v=0) band In the present study high-resolution FT emission spectrum high-resolution FT emission spectrum of the B 2  + (v’) - X 2  + (v’’) of the B 2  + (v’) - X 2  + (v’’) (v=0 and 1) band (v=0 and 1) band v=1 v=2 v=3 v=1 v=2 v=3

Experimental water pump Audio AMP. (1 kW) transformer (1:30) 3 k  He 75 kHz Quartz lends ( f = 50 mm ) (PNCl 2 ) 3 Heat resolution : 0.05 cm -1 spectral region : 31,700 – 50 cm -1 : 29,700 – 50 cm -1 accumulation time : 8 hrs. + +

B 2  + (v = 1) - X 2  + (v = 0) transition B 2  + (v = 1) - X 2  + (v = 0) transition N’’= P (N’’) R (N’’)

B 2  + (v = 0) - X 2  + (v = 1) transition N’’= P (N’’) R (N’’) 30

B 2  + (v = 0) - X 2  + (v = 1) transition P 1 (N’’) P 2 (N’’)

Molecular constants (unit : cm -1 ) state constant present study Ahmad and Hamilton B 2  + T e (14) (28)  e (10) 720.8(14)  e x e 1.80 B e (42) (28) 10 2  e (29) 2.4(7) 10 5 D e (28)  e  (15) X 2  +  e (39) (18)  e x e 7.62 B e (87) (28) 10 2  e (55) 1.5(12) 10 5 D e (40)  e (25)

Discussion Bond strength in B 2  + becomes weak ! Dissociation energy (eV) De =  e 2 /4  e x e state present study previous works B 2  (99) 3.1 X 2  (27) 4.96 incorrect values of  e x e ? parameter X 2  + B 2  + r e (A) (81) (45) k (N/m) (58) (82)

Potential energy curves Potential energy function V = T e + k/2(r  r e ) 2 + a(r  r e ) 3 + … V’ = D e [ 1 – exp(  (r  r e ) ) ] 2 Morse function Shallow well of the potential energy curve in B 2  +

Comparison with N 2 + and PN + Bond strength N 2 + : X 2  + g < B 2  + u PN + : X 2  + > B 2  + parameter X 2  + (g) B 2  + (u) r e (A) N PN P k (N/m) N PN P 2 + 

Electronic configuration PN + ion N 2 + ion Avoided crossing (6  *) 1 (2  ) 4 (7  ) 2 strong bond (6  *) 2 (2  ) 3 (7  ) 1 (3  *) 1 weak bond Bond strength in B 2  + of PN + becomes weak (4  *) 1 (1  ) 4 (5  ) 2 B 2  + u (strong bond) (4  *) 2 (1  ) 3 (5  ) 1 (2  *) 1 C 2  + u (weak bond) Bond strength in B 2  + u of N 2 + becomes strong 40,000 cm -1 <

Rotational perturbation Residuals in the least squares fitting of the (0-0) band

Rotational perturbation Residuals in the least squares fitting of the (0-1) band

B 2  + (v = 0) - X 2  + (v = 1) transition P 1 (N’’) P 2 (N’’)

Rotational perturbation Residuals in the least squares fitting of the (1-0) band

Summary 1. Ultraviolet emission spectrum of the B 2  + - X 2  + transition of the PN + ion was observed by FT spectruscopy. 2. Rotational analysis for the three vibronic bands, (1-0), (0-1), and (0-0), were performed to determined the molecular consants. 3. Potential energy curves for X 2  + and B 2  + were determined and the potential energy of B 2  + was confirmed to have a shallow well. 4. The molecular constants of B 2  + of PN + are different from those of N 2 + due to the difference of the electronic configuration of B 2  Rotational perturbations in the B 2  + vibronic states were observed.

Observed spectrum Nine vibronic bands of the A 2  + - X 2   transition Four vibronic bands of the A 2  + - X 2   transition A 2  + X 2  (000) (100) (010) (001) (100) (010) (001) 22 22 2   2   0 1,000 2,000 3,000 13,697 cm -1

Centrifugal disotortion constant D in X 2  3/2 D e = 4B e 3 /  e 2

Electronic configuration (3  ) 2 (1  ) 4 (4  ) 2 (2  ) 4 : BrCN (X 1  + ) (3  ) 2 (1  ) 4 (4  ) 2 (2  ) 3 : BrCN + (X 2  ) (3  ) 2 (1  ) 4 (4  ) 1 (2  ) 4 : BrCN + (A 2  + ) 2  : p (Br) –  (CN) 4  : p z (N) (non-bonding) Geometrical difference is small !

Renner parameter species A eff  2  79 BrCN +   (70)  (27) BO 2   86.4  0.19 CNC CO 2 +   96.8  NCO   76  0.14 N 2 O +   79.7 