Please use this identifier to cite or link to this item:
Title: Near-IR laser generation of a high-energy conformer of L-alanine and the mechanism of its decay in a low-temperature nitrogen matrix
Authors: Nunes, Cláudio M. 
Lapinski, Leszek 
Fausto, Rui 
Reva, Igor 
Issue Date: 28-Mar-2013
Volume: 138
Issue: 12
Abstract: Monomers of L-alanine (ALA) were isolated in cryogenic nitrogen matrices at 14 K. Two conformers were identified for the compound trapped from the gas-phase into the solid nitrogen environment. The potential energy surface (PES) of ALA was theoretically calculated at the MP2 and QCISD levels. Twelve minima were located on this PES. Seven low-energy conformers fall within the 0-10 kJ mol(-1) range and should be appreciably populated in the equilibrium gas phase prior to deposition. Observation of only two forms in the matrices is explained in terms of calculated barriers to conformational rearrangements. All conformers with the O=C-O-H moiety in the cis orientation are separated by low barriers and collapse to the most stable form I during deposition of the matrix onto the low-temperature substrate. The second observed form II has the O=C-O-H group in the trans orientation. The remaining trans forms have very high relative energies (between 24 and 30 kJ mol(-1)) and are not populated. The high-energy trans form VI, that differs from I only by rotation of the OH group, was found to be separated from other conformers by barriers that are high enough to open a perspective for its stabilization in a matrix. The form VI was photoproduced in situ by narrow-band near-infrared irradiation of the samples at 6935-6910 cm(-1), where the first overtone of the OH stretching vibration in form I appears. The photogenerated form VI decays in N2 matrices back to conformer I with a characteristic decay time of ∼15 min. The mechanism of the VI → I relaxation is rationalized in terms of the proton tunneling.
ISSN: 1089-7690
DOI: 10.1063/1.4795823
Rights: openAccess
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais

Files in This Item:
File Description SizeFormat
1.4795823.pdf1.15 MBAdobe PDFView/Open
Show full item record


checked on May 29, 2020

Citations 5

checked on Aug 2, 2022

Page view(s)

checked on Oct 4, 2022


checked on Oct 4, 2022

Google ScholarTM




Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.