Rotationally resolved spectroscopy and dynamics of the 3px 1A2 Rydberg state of formaldehyde

Abstract

The rotational structure of the lowest three vibrational levels (0⁰, 6¹ and 4¹) of the 3p_x ¹A₂ Rydberg state of formaldehyde has been studied by doubly-resonant three-photon ionization spectroscopy. A strong a-type Coriolis interaction between the in-plane rocking (ν₆) and out-of-plane bending (ν₄) modes results in the observation of vibronically forbidden transitions to the 6¹ level from the intermediate à ¹A₂ (2¹ 4³) level. The full widths at half maximum of the rovibronic transitions to the 4¹ state are considerably larger than to the vibrational ground state and the 6¹ level. The band origin (T₀ = 67 728.939(82) cm⁻¹), the rigid rotor rotational constants (A = 9.006(19) cm⁻¹, B = 1.331(20) cm⁻¹, and C = 1.135(22) cm⁻¹), the Coriolis coupling constant (ξ^a_4,6 = 8.86(89) cm⁻¹) and the deperturbed fundamental wave numbers of both vibrational modes (ṽ₆ = 808.88(25) cm⁻¹ and ṽ₄ = 984.92(26) cm⁻¹) have been determined for the 3p_x ¹A₂ Rydberg state. Polarization effects originating from the double-resonance technique have been exploited to detect the Coriolis interaction and investigate how it affects the predissociation dynamics.