Molecular Size Effect on the Site Dependent Photofragmentation of N and O K-Shell Excited CH₃CO(CH₂)_nCN (n = 0−3)

Abstract

Molecular size effects on the site specific photofragmentation of a core excited molecule were investigated by exciting the N and O K-shells for a series of CH3CO(CH2) n CN (n = 0−3) in which the O and N atoms were separated by successively inserting a CH2 group between the two atoms. The photofragment ions coincident with total photoelectrons were observed by means of a reflectron type time-of-flight mass spectrometer. Little difference was observed in the fragmentation patterns between the N and O K-edges in exciting CH3COCN, CH3COCH2CN, and CH3CO(CH2)2CN. Clear discrimination was observed in the long chained CH3CO(CH2)3CN.

Specific fragmentation of the K‐shell excited/ionized pyridine derivatives studied by electron impact: 2‐, 3‐ and 4‐methylpyridine

“…[1 -9] For the inner-shell excitation in gas phase site specificity is often found to be weak, [10] due to the competitive processes of site-specific fragmentation and intramolecular flow of excess energy into the whole molecule. The evidence was demonstrated in our previous studies on the inner-shell excitation of CF 3 CN, [11,12] CF 3 CCH, [13] CH 3 CO(CH 2 ) n CN (n = 0-3) [14] and CF 3 COCH 3 . [15] The extent of site specificity is correlated with the chain length of the molecules.…”

“…[15] The extent of site specificity is correlated with the chain length of the molecules. [14,15] Recently, we have reported the fragmentation process of a heterocyclic molecule, 2-amino-3-methylpyridine, following the C 1s and N 1s excitation/ionization by electron impact. [16] Yields of the fragment ions with m/e = 42 and 63 characteristically increase at the N K-edge, indicating the presence of the specific fragmentation channel(s) accessible through Auger transitions following the N 1s excitation/ionization.…”

Systematics of the gradient on the resonant core-hole state

“…1; the gradients at the equilibrium geometry of the ground state are listed in Table 2. A fast scission of the C-N triple bond of acetonitrile with N(1s) −→ π * (CN) excitation has been reported [22], and specific chemical reactions following core-excitation such as sudden C-N bond scission have been observed for other molecules that include a C-N triple bond [23,24]. We see that the first resonant state has the most negative gradient in the FC region at the N K-edge, which is assigned to N(1s) −→ π * (CN) excitation.…”

“…3. As typical examples, X * -H, C * -X, and C-N * cases are illustrated, Previous studies have examined the molecular size effect of the chemical reaction following core-excitation both experimentally [23,24] and theoretically [27,28]. Those studies showed that the site-specificity of chemical reaction following the core-excitation in the molecule is decreased by some CH 2 functional groups, to which the target functional groups are connected by a single bond.…”

Specific fragmentation of the K-shell excited/ionized aniline molecule studied by electron impact

“…Excitation of molecules at the K-shell level has attracted much attention for the last three decades, because site-specific fragmentation processes were observed in various molecular systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Inner-shell excited or ionized molecules dissociate into fragment ions following Auger electron emission.…”