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

Abstract

The rotational structure of the lowest three vibrational levels (0(0), 6(1) and 4(1)) of the 3p(x) (1)A(2) 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 (ν(6)) and out-of-plane bending (ν(4)) modes results in the observation of vibronically forbidden transitions to the 6(1) level from the intermediate Ã(1)A(2) (2(1) 4(3)) level. The full widths at half maximum of the rovibronic transitions to the 4(1) state are considerably larger than to the vibrational ground state and the 6(1) level. The band origin (T(0) = 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 = 8.86(89) cm(-1)) and the deperturbed fundamental wave numbers of both vibrational modes (v[combining tilde](6) = 808.88(25) cm(-1) and v[combining tilde](4) = 984.92(26) cm(-1)) have been determined for the 3p(x) (1)A(2) 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.

The formaldehyde cation: Rovibrational energy level structure and Coriolis interaction near the adiabatic ionization threshold

“…tive of an a-type Coriolis interaction between the 4 1 and 6 1 vibrational states as also observed in the neutral ground state [7,11,12] and the 3p x Rydberg state [9] of CH 2 O. The strength of the Coriolis coupling and the separation (>200 cm À1 ) between the interacting vibrational levels results in effective A + constants that differ significantly from each other rather than in a local perturbation of the rotational states around a given K þ a value [23].…”

“…Because in a first approximation the rovibronic energy level structure of unperturbed Rydberg states closely resembles that of the cation, the present analysis was also instructive for the assignment of the vibronic structure of the 3p x Rydberg state of neutral formaldehyde [9]. The 3p x state is known to be the only member of the 3p complex with a well-behaved energy level structure [5,8].…”

“…3(a) and (b) were recorded via the 2 2Kc and 3 2Kc rotational levels (indicated above each trace on the left) of the 3p x 6 1 and 3p x 4 1 intermediate states, respectively. The K c substructure of the intermediate 3p x state could not be resolved experimentally because of the rapid predissociation [9]. The spectra in Fig.…”

“…The vibronically forbidden 3p x ð6 1 Þ½C ev ¼ B 1 e A ð2 1 4 3 Þ½C 0 ev ¼ B 2 transition draws its intensity from an a-type Coriolis interaction of the 3p x 6 1 (in-plane rocking) level with the 3p x 4 1 (out-of-plane bending) level which is accessible from the e A ð2 1 4 3 Þ level as will be discussed in more detail in Ref. [9]. 2.…”

“…Since this pioneering study of the e A 1 A 2 e X 1 A 1 band system, extensive and comprehensive studies of the rotational structure and vibronic dynamics of the electronic ground [2][3][4] and electronic excited states [5][6][7][8][9] of neutral CH 2 O have been performed. In particular, the rovibrational structure of the polyads in the 3.5 lm [10] and 5-10 lm (see Refs.…”