Fourier-transform microwave spectroscopy of the CCCCl radical Takashi Yoshikawa, Yoshihiro Sumiyoshi, and Yasuki Endo Graduate School of Arts and Sciences, The University of Tokyo

Introduction Previous spectroscopic studies of the C n Cl radicals CCl CCCl CCCCl C 4 Cl Electronic absorption in Ne matrix C 2n Cl C 2n+1 Cl Sumiyoshi et al. JCP, 119, 1246 (2003) Sumiyoshi et al. CPL, 414, 82 (2005) Wijingaaden et al. JPC, A108, 4219 (2004) Endo et al. JMS, 94, 199 (1982) Wijingaaden et al. JPC, A109, 5553 (2005) C 6 Cl Wijingaaden et al. JPC, A108, 4219 (2004) C 5 Cl FTMW Electronic absorption in Ne matrix mmW Electronic absorption in Ne matrix No high resolution data!!!

Introduction Electron configurations of C n Cl CCl CCCl CCCCl C 4 Cl C 2n Cl C 2n+1 Cl In the limit of linearity 66 22 77 33 22 11  44 33 88 22 99 33 33 13  44 22

Introduction Potential energy surfaces of C n Cl CCl CCCl CCCCl C 4 Cl C 2n Cl C 2n+1 Cl In the limit of linearity       200 cm cm cm cm -1 

Experimental Set-up Sample gas PDN MW FID Cavity C 2 H % CCl % in Ne Condition Voltage 2.0 kV Stagnation Pressure 6.0 atm Chamber Pressure 1.5×10 -5 Torr Scan region from 11.3 to 33.8 GHz (pulsed-discharge nozzle)

Rotational spectra Observed transitions CCC 35 ClCCC 37 Cl from N = 2 ̶ 1 to N = 6 ̶ 5 45 lines34 lines N = 3 ̶ 2 35 Cl 37 Cl Including fine and hyperfine structures

Stick diagram N = 3 ̶ 2 N = 2 ̶ 1 N = 4 ̶ 3 N = 5 ̶ 4 N = 6 ̶ 5 CCC 35 Cl CCC 37 Cl

Analysis 2  Hamiltonian Observed spectral pattern 2  type Integer quantum number N observed rotational transitions

Results CCC 35 ClAb initio(CCC 35 Cl )CCC 37 Cl B (60) (57) D (11) (11)  (59) (10)  D (15) (15) b F 31.00(36) (32) c (19) (10) eQq (34) (24)  (kHz) Molecular constants of the CCCCl radical (MHz) RCCSD(T)/cc-pVQZ QCISD/cc-pVTZ

Discussion dipole-dipole constants The determined c constant is negative!(-29 MHz) The ground electronic state is  !!! Unpaired electron orbital on the Cl atom extends… perpendicular (  ) or parallel (  ) to the molecular axis The c constant negative positive

Renner-Teller effect Molecular structure ●The observed spectral pattern is 2  ●The ground electronic state is 2  in the limit of linearity. ●Molecular structure is bent!!! ●The observed transitions are a -type transitions with K a = 0. Strong Renner-Teller effect 2 A'X ～ 22 2 A"A ～

Molecular structure Ab initio calculation RCCSD(T)/cc-pVQZ 2 A'X ～ Dipole moment 3.7 D D aa bb A MHz B MHz C MHz MHz (B+C)/ MHz Exp.

Linearity linear bent Experiment b F c eQq  B+C)/ In MHz bent structure!!! Ab initio calculation RCCSD(T)/cc-pVQZ QCISD/cc-pVTZ Ab initio calculation support…

Potential energy surface Barrier = 1000 cm -1 Vertical = 5400 cm -1 RCCSD(T)/cc-pVTZ

C n Cl series Hyperfine constants of C n Cl CClCCCl CCCCl C 4 Cl b F c g  g N  N eQq  In MHz same tendencies for C 2n Cl and C 2n+1 Cl series!!! eQq and  indicate…

C n Cl series Molecular structures of the C n Cl radical RCCSD(T)/cc-pVTZ 2  -type transitions were observed! Future work 2  -type transitions are expected!! Arulmozhiraja et al. JCP (2006)

Summary ●Rotational spectra have been observed by FTMW for the first time. CCCCl ●Experimental information on molecular structure has been obtained for the first time.

Isotope factor Hyperfine constants Ratio of the nuclear magnetic dipole moments for the 35 Cl and 37 Cl Ratio of the electronic quadrupole moments for the 35 Cl and 37 Cl  37 /  35 = 0.83 Q 37 / Q 35 = 0.79 b F = 0.86 c  = 0.83 eQq  = 0.80 Exp.

Molecular structure Linearity of CCCCl Normalized centrifugal distortion constant CCCClCCCSHCCCS 4.6× MHz × MHz × MHz -2 Yamamoto et al. APJL 317 L119 (1987) Hirahara et al. JPC (1994) Not linear!!!