MASS-SELECTIVE MATRIX-ISOLATION SPECTROSCOPY: FT-IR SPECTRA OF CYANOACETYLENE AND TETRACYANOETHYLENE IONS AND THEIR IONIC FRAGMENTS

$^{a}$A.M. Smith-Gicklhorn, M. Lorenz, R. Kolos and V.E. Bondybey J. Chem. Phys. 115, 7534-7542 (2001). $^{b}$A.M. Smith-Gicklhorn, M. Frankowski, and V.E. Bondybey Phys. Chem. Chem. Phys. In Press. $^{c}$A.M. Smith-Gicklhorn, M. Lorenz, M. Frankowski, R. Kolos and V.E. Bondybey Chem. Phys. Lett. 351, 85-91 (2002).Author Institution: Institut f\""{u}r Physikalische und Theoretische Chemie; Institute of Physical Chemistry of the Polish Academy of Sciences, Institut f\""{u}r Physikalische und Theoretische ChemieRecent spectroscopic results from a new setup for the deposition of mass-selected ions in neon matrices are presented. Gaseous precursor substances are ionized in a homebuilt electron impact source, the ions extracted and deflected by $90^{\circ}$ into a quadrupole mass filter with unity mass resolution up to 500 amu. The mass-selected cations are deposited simultaneously with an excess of electrons, to maintain overall sample neutrality and prevent buildup of space charges, and neon gas onto a reflective substrate held at 7 K. Fourier-transform infrared spectra from such samples using cyanoacetylene and tetracyanoethylene reveal new infrared transitions for several cations. The strong infrared signal observed for the asymmetric stretch of $CNC^{+}$ and the appearance of the corresponding band for $^{13}CNC^{+}$ in its natural isotopic abundance, demonstrates the sensitivity and usefulness of the apparatus. A combination band of $CNC^{+}$ is also observed, revealing its low-frequency bend. Using this setup, the infrared spectra of cyanoacetylene $ions^{a}$ $(H(D)C_{3}N^{+}$ and $C_{3}N^{+}_{2}$) and tetracyanoethylene ions and ionic $fragments^{b}$ $(C_{6}N^{+}_{4}$, $C_{6}N^{-}_{4}$, $C_{6}N^{+}_{3}$, $C_{5}N^{+}_{3}$, and $C_{3}N^{+}_{2}$) are observed for the first time. The assignment of the numberous observed vibrations of these ions are well-supported by our density-functional calculations. Using this apparatus and the sensitive LIF techique, the assignment of a rich emission spectrum with origin near 440 nm is confirmed to be due to mass 88 or $C_{5}N_{2}$ $neutral^{c}$ as subsequently verified by a cavity ringdown measurement of Linnartz, Maier et al