The distribution Pε of internal energies deposited in W(CO)6 (+•). ions upon charge stripping (that is, electron detachment to yield the doubly charged ion in the course of a single kiloelec-tronvolt energy collision) was estimated by a thermochemical method from the measured relative abundances of the doubly charged fragment ions produced. The thermochemical information needed to estimate P/ge was obtained by measuring the threshold translational energy losses associated with charge stripping of the singly charged fragment ions, W(CO) n (+) (n = 0-5). The P(/ge) curve falls exponentially with increasing internal energy. The average energy transferred to W(CO)6 (+•) upon a 7.8-keV collision with O2 is 19 eV, yielding W(CO)6 (2•) ions with an average of 4 eV of internal energy. In its general appearance, the P(ε) distribution associated with charge stripping is similar to the curves obtained from simple collisional activation of either W(CO) 6 (+•). or W(CO)6 (2+•) in kiloelectronvolt energy gaseous collisions. Given that charge stripping occurs by way of an electronic excitation process, this similarity in the energy deposition function is taken to indicate that electronic excitation is also the major mechanism for simple collisional activation in this system at zero scattering angle in the kiloelectronvolt energy regime. The internal energy distribution associated with a related charge-stripping process, charge inversion from the metal carbonyl anions to yield the corresponding cations, was also recorded. This reaction shows a large (∼7 eV) average internal energy deposition with a distribution that indicates near-zero probability of formation of unexcited ions. These data are tentatively interpreted in terms of vibrationalelectron detachment. The internal energy distribution associated with an exothermic process, charge exchange [W(CO)6 (2+•) + O2 → W(CO) + (6•)+O2 (+•)], was also characterized. Unexpectedly strong coupling of translational to internal energy is observed, and there is a large probability of depositing internal energies in excess of 10 eV, even though the exothermicity is only 3 eV. Finally, the internal energy distributions associated with the formation of doubly charged W(CO)6 (2+•) ions by electron ionization have been measured. Unlike the distribution for charge stripping, but like that for singly charged ions generated by electron impact, this distribution shows considerable structure, presumably due to Franck-Condon factors.

The mass spectra of twenty-eight monosubstituted trans-stilbenes in ortho, meta, para and alpha positions with -N(and -NOz groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M -Substituent] ion. In o-nitro-, o-methoxy-, cc-carboxyl-and * Reported in part at the 2nd Conference on Mass Spectrometry, CCR Euratom, Ispra, Italy, 1st to 3rd September 1971, EUR 4765, 239 (1972. 323 22 * The correct nomenclature for the proposed structure b* is asymmetric indacenyl cation.

Electron ionization (EI),In the last few years several papers have dealt with the mass spectral differentiation of anomeric nucleosides,',2 g l y c~s i d e s~.~ and disac~harides.~, Fast-atom bombardment (FAB) mass spectra and spectra produced by FAB coupled with tandem mass spectrometry (MS/MS) of diastereoisomeric glycosylazide derivatives have been r e p~r t e d .~In the FAB spectra, pronounced fragment peaks were observed indicating the loss of hydrogen azide HN, from the protonated molecules. Differentiation between the azides studied is mainly based on the examination of collision-inducedfragment ions. Carbohydrate derivatives and some other organic azides have been investigated by desorption chemical ionization (DCI) and FAB.8 It was found that under these ionization conditions, the azido group can undergo reduction to an amino group. This was deduced from the appearance of an [MH-261' ion. This ion is formed after elimination of the nitrogen molecule from MH+ ions by subsequent reduction of the resulting [MH -N2]+ ions by hydrogen radicals in the ion source.'These studies have shown that the fragmentation patterns of several organic azides can differ widely, depending on the mass spectral technique used. However, there are many examples showing that it is possible to distinguish the anomers unambiguously by mass spectral methods.Here we report a mass spectral investigation of anomeric 2,3-@isopropylidene a-and 0-D-ribofuranosyl azide derivatives, configurations of which are depicted below. The compounds la, lb, 5a and 5b are important synthetic starting azides to be transformed, for example, into triazolo ribonucleo~ides.~ To establish the origin of the most important ions appearing in the electron ionization (EI) mass spectra of l a and l b their deuterium-labelled derivatives (2-4) have also been examined. EXPERIMENTALThe syntheses of compounds 1 and 5 have been describedpreviously . 92,3-0-Isopropylidene (hexadeuter0)-Author to whom correspondence should be addressed. $H,OR' CH2OR'COC&jNOZ-p CH3 Sb a-D-ribofuranosylazide (3a) and 2,3-@isopropylidene-(hexadeuter0)-P-D-ribofuranosyl azide (3b) were prepared by the I2 catalyzed procedure" using hexadeuteroacetone in more than 80% yield as colorless liquids. Compounds 2 and 4 were obtained by hydrogendeuterium exchange in the hydroxyl group of 1 and 3, respectively. This was done by repetitive adding (and drying) of D 2 0 to the sample in the probe capillary.All mass spectral measurements were performed with an AutospecQ mass spectrometer of EBEqQ configuration (Fisons, VG Analytical, Manchester, UK). The samples were introduced via a direct-sample probe. Ammonia chemical ionization (CI) was carried out at an ammonia gas pressure that resulted in great excess of [NH,]' relative to [NH4NH3]+. The pressure conditions in methane CI were such that nearly equal amounts of CH; and C2H; were produced. RESULTS AND DISCUSSION EI mass spectraThe EI mass spectra of 1 to 4 are presented in Fig, 1 and those of the anomers of 5 in Fig. 2. The origin of the most importan...

"he unimolecular charge separation fragmentations of doubly charged benzene and 18 derivatives containing various numbers of íluorine, chlorine and bromine atoms have been studied. in the majonty of cases two dktinct b d s of transition state can be characterized, in one of which the ring system r e m e intact and in the other of which a lioear transition state ion is formed. There is evidence for rearrangement of haiogens both around the ring and aiong the linear chain.