The infrared multiphoton dissociation (IR MPD) of
formic acid molecules (HCOOH → CO + H2O)
with
free electron laser radiation in the 3 μm region (C−H stretch
vibrational absorption band) and in the 6 μm
region (CO stretch vibrational absorption band) has been achieved
using the same laser. Results indicate
that initial excitation of this dimer is more efficient for MPD then
initial monomer excitation. Carbon isotope-selective MPD has been performed with an isotopic mixture,
H12COOH + H13COOH (50% + 50%),
at an
irradiating wavelength of 5.56 μm. For this mixture, isotopic
selectivity s =
k
12/k
13 = 23 has been
attained
as a ratio of the rate constants of the H12COOH MPD
and the H13COOH MPD, respectively. The
isotopic
selectivity for 13C in the naturally occurring mixture
(1.1% of 13C-containing molecules) s =
k
13/k
12 = 22
has
been attained at an irradiating wavelength of 5.90 μm.