Laser induced fluorescence spectroscopy of the C3N radical

Electronic spectra of the C3N radical have been observed for the first time in the near ultraviolet wavelength region by laser induced fluorescence (LIF) spectroscopy. Seventeen vibronic bands of the (B) over tilde (2)Pi(i)-(X) over tilde (2)Sigma(+) electronic transition system of C3N were identified in LIF spectra of products in a discharge of HC3N. The origin of the (B) over tilde (2)Pi(i) state was determined to be 27 929.985(1) cm(-1) from rovibrational analyses. It was found that observations of two types of (2)Sigma vibronic levels, which have (2)Sigma(+) and (2)Sigma((+/-)) symmetries originated from excitations of the nu(4) trans-bending mode (omega(4)=369.1(20) cm(-1)) with a large Renner-Teller (RT) interaction (epsilon(4)=-0.1549(50)), and the nu(5) cis-bending mode (omega(5)=163.24(84) cm(-1)) with a small Renner-Teller interaction (epsilon(5)=-0.0503(68)), respectively. Vibronic levels, with excitations of the C-C stretching (omega(3)=869.7 cm(-1)) mode, were also identified. The spin-orbit interaction constant was determined to be A(so)=-36.7(50) cm(-1) from the RT analysis. In dispersed fluorescence spectra from (B) over tilde (2)Pi(i), vibrational structures of the low-lying electronically excited (A) over tilde (2)Pi(i) state were clearly observed with a strong progression due to the nu(3)' mode, together with those of the (X) over tilde (2)Sigma(+) state with weak intensities. The origin of (A) over tilde (2)Pi(i), T-0=1844(3) cm(-1), and the vibrational frequencies, omega(3)'=883(3) cm(-1) and omega(5)'=121(3) cm(-1) for (A) over tilde (2)Pi(i), and omega(3)''=1054(3) cm(-1), omega(4)''=405(3) cm(-1), and omega(5)''=131(3) cm(-1) for (X) over tilde (2)Sigma(+), were determined. Time profiles of fluorescence from (B) over tilde (2)Pi(i) have short (50-200 ns) and long (>1 mu s) decay components with quantum beats, indicating that there is a competition between radiative decay and the nonradiative internal conversion to vibrationally highly excited (A) over tilde (2)Pi(i) and (X) over tilde (2)Sigma(+). (c) 2007 American Institute of Physics.