Electric dipole moment of formaldehyde in the first ³<i>A</i>₂ excited state

Abstract

The Stark effect on the rotational lines of the 1 + –0 band of the 3 A 2 – 1 A 1 (π* ← n) transition of formaldehyde has been studied using field strengths up to 25 kV/cm. Measurements of the Stark splittings and shifts for the Q 3 (3, 3), R 2 (3, 3), Q 2 (3, 3), and Q 2 (5, 5) lines in parallel polarization lead to a value of 1.29 ± 0.03 D for the dipole moment of formaldehyde in its 3 A 2 -excited state. This value is significantly smaller than the value (μ′ = 1.56 ± 0.07 D) obtained by Freeman and Klemperer for the corresponding 1 A 2 -excited state. A few measurements on lines of the 0 + –0 band of the 3 A 2 – 1 A 1 system show that the Stark splittings and shifts are closely similar (± 3%) to those for the 1 + –0 band.The spin constants for the 3 A 2 state have been redetermined and are:[Formula: see text]The Stark splittings show conclusively that the line assigned in earlier work as R 1 (3, 3) is indeed a Q 2 (3, 3) line in agreement with the intensity formulas of Hougen.