TY - JOUR

T1 - Atmospheric photochemical loss of H and H2 from formaldehyde

T2 - the relevance of ultrafast processes

AU - Simonsen, Jens Bæk

AU - Rusteika, Nerijus

AU - Johnson, Matthew Stanley

AU - Sølling, Theis Ivan

PY - 2008

Y1 - 2008

N2 - We have performed ab initio calculations to examine the potential energy along the normal modesof ground-state HCHO and along the reaction coordinates for loss of H2 and atomic hydrogen,respectively. This exploration showed that there are no specific features that will lead to reactionon the excited-state surfaces for excitations that are relevant to the troposphere and stratosphere.The calculations did however lead to the localization of a conical intersection point throughwhich a specific loss of H2 could take place. However, the conical intersection lies at 5.4 eVrelative to the ground state molecule at equilibrium and is thus inaccessible via single photonexcitation at tropospheric and stratospheric wavelengths. In addition to the ab initio investigationwe have carried out a femtosecond pump–probe experiment using a 266/400 nm excitation. Theresults show that the timescale for the internal conversion from the initially prepared high-lyingRydberg states is on the order of a picosecond. This process populates the n - p* first excitedsinglet state which then survives for a substantially longer time before it is depopulated to formhot ground state or triplet-excited molecules that can then decompose.

AB - We have performed ab initio calculations to examine the potential energy along the normal modesof ground-state HCHO and along the reaction coordinates for loss of H2 and atomic hydrogen,respectively. This exploration showed that there are no specific features that will lead to reactionon the excited-state surfaces for excitations that are relevant to the troposphere and stratosphere.The calculations did however lead to the localization of a conical intersection point throughwhich a specific loss of H2 could take place. However, the conical intersection lies at 5.4 eVrelative to the ground state molecule at equilibrium and is thus inaccessible via single photonexcitation at tropospheric and stratospheric wavelengths. In addition to the ab initio investigationwe have carried out a femtosecond pump–probe experiment using a 266/400 nm excitation. Theresults show that the timescale for the internal conversion from the initially prepared high-lyingRydberg states is on the order of a picosecond. This process populates the n - p* first excitedsinglet state which then survives for a substantially longer time before it is depopulated to formhot ground state or triplet-excited molecules that can then decompose.

U2 - 10.1039/b712757j

DO - 10.1039/b712757j

M3 - Journal article

VL - 10

SP - 674

EP - 680

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

ER -