Selenoketene (H 2 CCSe) +• and selenoketyl cumulene (HCCSe) + ions and their neutral counterparts: a tandem mass spectrometric and computational study

Dissociative electron ionization (70eV) of selenophene (C 4 H 4 Se) generates m / z 106 ions of composition [H 2 , C 2 , 80 Se] +• and m / z 105 ions of [H, C 2 , 80 Se] + . From tandem mass spectrometric experiments, Density Functional Theory (DFT) and ab initio calculations, it is concluded that these ions have the structure of selenoketene H 2 CCSe +• (1a +• )and selenoketyl HCCSe + (2a + ) ions respectively. The calculations predict that selenoketene ion 1a +• is separated by high energy barriers from its isomers selenirene (H $\catcode`@=11 \def\overlsqmatrix#1{\null\vbox{\normalbaselines\m@th \ialign{\hfil$##$\hfil&&\quad\hfil$##$\hfil\crcr \mathstrut\crcr\noalign{\kern-\baselineskip} #1\crcr\mathstrut\crcr\noalign{\kern-\baselineskip}}}} \newdimen\rulwidth \def\downsqbrace#1{\setbox1=\hbox{#1} \rulwidth=\wd1\advance \rulwidth by -6pt \raise3pt\hbox{$\overlsqmatrix{\vrule height5pt\kern-0.5pt\raise5pt\hbox to \rulwidth{\hrulefill}\kern-0.5pt\vrule height5pt\cr\noalign{\vskip-3pt}\hbox{#1}\cr\noalign{\vskip-5pt}}$}} \catcode`@=12 \downsqbrace{{\rm CCHS}}$ e) +• 1b +• , ethyne selenol (HCCSeH) +• 1c +• , (CCHSeH) +• 1d +• and (CCSeH 2 ) +• 1e +• . The selenoketyl ion 2a + is separated by high barriers from its isomers (CCHSe) + 2b + , and (CCSeH) + 2c + . Neutralization‐reionization mass spectra (NRMS) of these structurally characterized ions confirmed that the corresponding neutral analogues, selenoketene H 2 CCSe 1a and selenoketyl radical HCCSe 2a • are stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for selenoketene and selenoketyl ions and neutrals studied at B3LYP/6–31G(d,p) and G2/G2(MP2) levels are used to support and interpret the experimental results. Copyright © 2005 John Wiley & Sons, Ltd.