Rovibrational spectroscopy of formaldehyde in helium nanodroplets

Formaldehyde has been characterized in superfluid helium nanodroplets in the region of the symmetric (v(1)) and antisymmetric (v(5)) stretching bands. The band origins are blue shifted, consistent with a decrease in the dipole moment and polarizability in going from the ground to excited vibrational states, and the lines within each band are homogeneously broadened, with vibrational lifetimes of 26 and 6.2 ps for assigned transitions in the v(1) and v(5) bands, respectively. The A, B, and C constants are renormalized to 79%, 65%, and 49% of their gas phase values, corresponding to moments of inertia of helium, I-He of 0.488, 6.88, and 15.3 amu angstrom(2), about the inertial a-, b-, and c-axes, respectively. While partial breakdown of the adiabatic approximation is expected for rotations about the b- and c-axes, the small value of I-He about the a-axis is indicative of near complete breakdown. The larger value of I-He about the c-axis in comparison to the b-axis is attributed to the greater anisotropy of the interaction potential in the plane of H2CO [M.D. Wheeler, A.M. Ellis, Chem. Phys. Lett. 374 (2003) 392]. (C) 2013 Elsevier Inc. All rights reserved.