TOF-MS

TECHNICAL SPECIFICATIONS

• The TOF-mass spectrometer is equipped with:

• bakeable high vacuum chamber  in camera pari a 10-9 mbar);
• custom Wiley-McLaren time-of-flight (TOF) analyser (mass resolution of 1 amu up to about m/z 100);
• electron channel multiplier (CEM) e microchannel plates (MCP);
• stainless steel oven heated by a Thermocoax (up to 300°C);
  the oven can house a crucible to sublimate solid samples, or a gas line to transfer liquid/gaseous samples of sufficient vapor pressure from test tube located outside the vacuum chamber; 
  • VUV rare gas discharge lamp as photon source

    Gas	Pressure (mbar)	Energy (eV)	Current (pA)
    He	3x10-1	21.22	5
    Ne	3x10-2	16.67	3
    Ar	1x10-2	11.62	0.2
    Kr	1x10-2	10.00	0.2
    Xe	2.5x10-3	8.43	0.05

• electronics and signal processing (NIM standard)
• time-to-digital converter with multi-hit capabilities (ACAM)
• computer equipped with LabView and C++ for data acquisition and data analysis
• heating system to bake-out the apparatus
• the pulsed extraction can be implemented if needed

 

Case Studies

VUV photofragmentation of halogenated methanes and the atmospheric chemistry
 

Halomethanes are widely recognized anthropic species long living in the atmosphere, with potentially harmful impact on the ozone layer. The study of the photofragmentation of CH2X2 molecules (X=F, Cl, Br, I) and chlorinated methanes (CHnCl4−n with n = 0–3) using He, Ne, and Ar VUV discharge lamps can shine light on their chemistry in the upper atmosphere. The results have shown the peculiar behavior of the CH2F2 molecule which is the only dihalomethane to dissociate via the H-loss channel yielding CHF2+ ion and an H atom, with relevant atmospheric implications. Indeed, as fluorine reacts rapidly with atmospheric molecule to form HF, the reactive H atom can also affect the atmospheric environment via different chemical reactions with important molecules like ozone.
 
See: J. Chem. Phys. 140, 184307 (2014)

 

 

Alkyl phosphates and the H-bonding interactions.
 
Alkyl phosphates are used in chemical industry. Once released in the environment, they can become source of pollution, and several approaches have been proposed for their degradation, including UV/VUV light irradiation.
This work investigates the fragmentation mechanisms of alkyl phosphates in the VUV range. The results show that all the investigated substances have similar fragmentation patterns characterized by the stepwise cleavage of the C-O bond, which links the alkyl chains to the phosphate group, and lead to the formation of esters with a lower number of alkyl side chains and ending to the protonated orthophosphoric acid.  
 
See: Journal of Photochemistry & Photobiology A: Chemistry 365 (2018) 13–22

A gas-phase study of peptide bond formation/disruption.

The dynamic chemical process involving the coupling of the condensation ofα-aminoacids into peptides with the peptide degradation ‘returning’ individual aminoacids, may have provided an effective mechanism for reshuffling and building up the complexity of aminoacid sequences preceding the emergence of life.
Since these processes rely on the mechanisms of peptide bond formation and cleavage, we have undertaken a study of the peptide bond formation/disruption on the simplest peptides, the cyclic (c-) and linear (ℓ-) dipeptides in the gas phase, by photoionisation experiments.
The preliminary results suggest that a cyclisation process may happen during the TOF-MS measurements carried out on linear dipeptides. This process may be driven by the temperature in the condensed phase, the ‘electrostatic forces’ in the unstable zwitterion produced in the sublimation or the fast rearrangement of the highly reactive cation following ionisation.

Schematic of the ℓ- and c-dipeptides studied.