Renner Teller Components Research Articles

Ab Initio Studies of Radicals HBX (X=H, F, Cl, Br): Molecular Structure, Vibrational Frequencies and Potential Energy☆☆Supported by the National Natural Science Foundation of China under Grant Nos 11647011, 11605105 and 11604181, and the Shandong Provincial Natural Science Foundation of China under Grant No 2016ZRB01A38.

We describe high-level ab initio calculations on the BH2, HBF, HBCl and HBBr radicals. Molecular structure, vibrational frequencies and potential energy curves of the ground state and the first excited state, which are two Renner–Teller components for a 2Π state at linearity, are studied using the basis sets aug-cc-pVTZ and icMRCI+Q technique. On the basis of the potential energy curves, a reliable potential energy barrier to dissociation HB+X (X=F, Cl, Br) fragments and to linearity are given. The ab initio results will add some understanding on the spectrum and the photo-dissociation dynamics of the series of radicals.

An experimental and theoretical study of the Ã(2)A(″)Π-X̃(2)A(') band system of the jet-cooled HBBr/DBBr free radical.

The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr3 vapor and H2 or D2 in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra. HBBr has an extensive band system in the red which involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π state at linearity. We have used high level ab initio theory to calculate potential energy surfaces for the bent (2)A' ground state and the linear Ã(2)A(″)Π excited state and we have determined the ro-vibronic energy levels variationally, including spin orbit effects. The correspondence between the computed and experimentally observed transition frequencies, upper state level symmetries, and H and B isotope shifts was used to make reliable assignments. We have shown that the ground state barriers to linearity, which range from 10 000 cm(-1) in HBF to 2700 cm(-1) in BH2, are inversely related to the energy of the first excited (2)Σ ((2)A') electronic state. This suggests that a vibronic coupling mechanism is responsible for the nonlinear equilibrium geometries of the ground states of the HBX free radicals.

An experimental and theoretical study of the electronic spectrum of the HBCl free radical.

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the Ã(2)A(″)Π-X̃(2)A(') band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl3 and H2 or D2 in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground and excited state vibrational energy levels. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π electronic state at linearity. We have used high level ab initio theory to calculate the ground and excited state potential energy surfaces and have determined the vibronic energy levels variationally. The theory results were used to assign the LIF spectra which involve transitions from the ground state zero-point level to high vibrational levels of the excited state. The correspondence between theory and experiment, including the transition frequencies, upper state band symmetries, and H, B, and Cl isotope shifts, was used to validate the assignments.

Generation of full dimensional potential energy surfaces for atmospherically important charge transfer tetratomic complexes: the case of the OMgOO+ radical cation

The weakly bound charge transfer OMgOO(+)((2)Π) ion is a quasi-linear-bent Renner-Teller system with a non-zero spin-orbit contribution. The six-dimensional potential energy surfaces (6D-PESs) for the two Renner-Teller components have been generated in internal coordinates. After benchmarking calculations, we show that the newly implemented explicitly correlated coupled cluster approach (RCCSD(T)-F12) in connection with the cc-pVTZ-F12 basis set provides an accurate description of the full 6D-PESs of this molecular system. Both components are bent with low barriers to linearity along the in-plane angles. The potentials are also very flat along the out-of-plane torsional mode. Hence, this confers a pronounced quasi linear character to OMgOO(+). Moreover, the parts of the potentials relative to the middle bond are shallow and strongly coupled to the bending motions. The parts of the PESs corresponding to the OO and MgO external diatom stretch coordinates differ strongly from those relative to the four other internal coordinates. Special care was taken to correctly account for such behaviors during the generation of the grid and fitting procedures. The present theoretical methodology can be used for mapping the 6D-PESs of other atmospherically important charge transfer complexes presenting similar features such as ONNO(+), O4(+), OOCO(+) or M-CO2(+) (where M is an alkali, magnesium or aluminum metal).

Spectroscopic properties of the low-lying electronic states of RbHen (n = 1, 2) and their comparison with lighter alkali metal-helium systems

Ab initio-based configuration interaction studies on RbHe and He–Rb–He have explored some key features of the low-lying electronic states of these van der Waals systems. The radiative lifetime of the Rb*He exciplex has been calculated to be around 24.5 ns, which is slightly higher than the HeRb*He lifetime (∼20 ns) and lower than the atomic fluorescence lifetime of Rb, by roughly 3.5 ns. Better exciplex stability of the symmetric triatomic system is evidenced by its higher binding energy value in comparison to the diatomic system by a substantial margin. BSSE-corrected spin–orbit calculations of RbHe have predicted a potential barrier of the 12Π1/2 state with a height of 15 cm−1 and width of 2.57 Å. The 2Πu state of the triatomic molecule shows a conical intersection of its Renner–Teller components (12A1 and 12B2) near a 99° bond angle along the bending path. Their unstable higher excited states (12Σ+1/2 or 12Σ+g,1/2) can trigger the pumping of the blue side of the ns2S1/2 → np2P3/2 transition, and this may eventually lead to the np2P1/2 →ns2S1/2 lasing transition. The broad fluorescence band with a peak near 11 900 cm−1 is found to arise from the 12Π3/2–X2Σ+1/2 transition of RbHe.

Millimeter-wave rotational spectroscopy of FeCN (X 4Δi) and FeNC (X 6Δi): Determining the lowest energy isomer

The pure rotational spectrum of FeCN has been recorded in the frequency range 140-500 GHz using millimeter/sub-millimeter direct absorption techniques. The species was created in an ac discharge of Fe(CO)(5) and cyanogen. Spectra of the (13)C, (54)Fe, and (57)Fe isotopologues were also measured, confirming the linear cyanide structure of this free radical. Lines originating from several Renner-Teller components in the ν(2) bending mode were also observed. Based on the observed spin-orbit pattern, the ground state of FeCN is (4)Δ(i), with small lambda-doubling splittings apparent in the Ω = 5/2, 3/2, and 1/2 components. In addition, a much weaker spectrum of the lowest spin-orbit component of FeNC, Ω = 9/2, was recorded; these data are consistent with the rotational parameters of previous optical studies. The data for FeCN were fit with a Hund's case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling parameters were determined. Rotational constants were also established from a case (c) analysis for the other isotopologues, excited vibronic states, and for FeNC. The r(0) bond lengths of FeCN were determined to be r(Fe-C) = 1.924 Å and r(C-N) = 1.157 Å, in agreement with theoretical predictions for the (4)Δ(i) state. These measurements indicate that FeCN is the lower energy isomer and is more stable than FeNC by ~1.9 kcal/mol.

The complex spectrum of a “simple” free radical: The ${\rm \tilde A}$Ã-${\rm \tilde X}$X̃ band system of the jet-cooled boron difluoride free radical

The near-ultraviolet band system of the jet-cooled boron difluoride free radical has been studied by a combination of laser-induced fluorescence and single vibronic level wavelength resolved emission spectroscopies. The radical was produced in a supersonic discharge jet using a precursor mixture of 1%-3% of BF(3) or (10)BF(3) in high pressure argon. A large number of bands were found in the 340-286 nm region and assigned as transitions from the X̃(2)A(1) ground state to the lower Renner-Teller component of the Ã(2)Π excited state, based on our previous ab initio potential energy surface predictions, matching the emission spectra Franck-Condon profiles of (11)BF(2) and (10)BF(2), and comparison of observed and calculated boron isotope effects. Several bands have been rotationally analyzed providing ground state structural parameters of r(0)('') (BF) = 1.3102(9) Å and θ(0)('') (FBF) = 119.7(6)°. The ground state totally symmetric vibrational energy levels of both boron isotopologues have also been measured and assigned up to energies of more than 8000 cm(-1). Although BF(2) might be considered to be a "simple" free radical, understanding the details of its electronic spectrum remains a major challenge for both theory and experiment.

The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra

Subsequent to our spectroscopic detection of the HBX (X=F, Cl, Br) free radicals (S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)), the electronic spectrum of the A (2)A(")Pi-X (2)A(') system of the fluoroborane (HBF) radical in the 600-745 nm region has been studied in detail using the pulsed discharge jet technique. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Pi state at linearity. Using the results of our theoretical study of the ground and excited state vibrational energy levels and (11)B-(10)B isotope shifts (see the companion paper), the vibrational quantum numbers of the bands in the laser-induced fluorescence (LIF) spectra have been assigned. Rotational and vibrational analyses of the LIF and wavelength resolved emission spectra have been carried out, from which the linear excited state and the bent ground state equilibrium configurations have been confirmed. The ground state molecular geometry of HBF has been determined as r(0)(BH)=1.214(2) A, r(0)(BF)=1.303 4(5) A, and theta=120.7(1) degrees. Based on high-level ab initio calculations and symmetry considerations, predissociation of the excited state into H((2)S)+BF((1)Sigma(+)) on the ground state potential energy surface is identified as the cause of the breaking off of fluorescence in the LIF spectra.

Electronic structure and spectroscopy of the ground and excited states of the HMgO and HMgS radicals

Ab initio RCCSD(T) and MRCI calculations have been carried out for the stable isomer forms of magnesium monohydroxide, HMgO and monohydro sulfide, HMgS. For both molecular systems, it is found that the electronic ground state is a (2)Pi(i) state with linear/linear Renner-Teller components. At the equilibrium geometry of the ground states, the spin-orbit constants A(SO) have been calculated -123 cm(-1) for HMgO and -312 cm(-1) for HMgS. Along the isomerisation path towards the more stable structures MgOH and MgSH, the (2)A' component of the Renner Teller pair correlates with the ground state and the (2)A component with an excited state. Using RCCSD(T) potential energy functions and a variational Renner-Teller approach, rovibronic levels of the X(2)Pi state of both systems have been evaluated for J = 1/2 and 3/2. Strong Fermi resonances are found in HMgO, but not in HMgS. The first electronically excited (2)Sigma(divided by) states are calculated (T-e value at RCCSD(T) level) to lie 8041 cm(-1) above the ground state for HMgS and 4935 cm(-1) for HMgO. (C) 2003 Elsevier B.V. All rights reserved.

The asymptotic region of the potential energy surfaces relevant for the O(3P)+O2(X 3Σg−)⇌O3 reaction

The potential energy functions for all states of ozone correlating with the lowest O(3P)+O2(X 3Σg−) asymptote have been calculated in the asymptotic region employing correlated electronic wave functions. For linear ozone, the Σs states (s=1,3, and 5) lie above the corresponding Πs states. For bent geometries the Π states split into Renner–Teller components with A′ and A″ symmetry, respectively. While the Π1 and Π3 states lead to bent–bent Renner–Teller pairs, the Π5 state gives rise to a linear/linear pair of states. The different spin multiplets emerging from the Π states cross for valence angles around 160° and the A′1 component becomes the lowest one. The matrix elements of the spin-orbit operator have also been calculated. They are dominated by the atomic P3 contributions and their dependence on the mutual orientation of the O2 molecule and the O atom is small. In the regions where the states correlating to the linear Π1,3,5 cross, i.e., for valence angles between 150° and 180° and close to 90°, the mixing among the singlet, triplet, and quintet states is strong and the electron spin quantum number is no longer a good quantum number.

The near ultraviolet spectrum of the FCO radical: Re-assignment of transitions and predissociation of the electronically excited state

Cavity ring-down spectra of the FCO radical, recorded over the wave number range 29 500–31 600 cm−1 reveal rotational structure of the electronically excited state for the first time. The spectra demonstrate the need for a complete re-assignment of the vibronic features: The rotationally resolved bands are successfully simulated as arising from c-type transitions from the ground X̃ 2A′ state to the linear A19″ component of the à 2Π state. The bands are attributed to two overlapping vibrational progressions: one progression involves excitation of the F–C–O bending mode (v3′), the other consists of a combination of v3′ and one quantum of the C–F stretch (v2′). Sharp rotational structure is only observed for sub-bands with K′=0; bands with K′>0 are diffuse, indicating rapid, rotation induced predissociation. Band origins, rotational constants for the excited state, and spectral linewidths have been derived from the K′=0–K″=1 sub-bands. All rotational lines are somewhat broadened and there is evidence of linewidths that increase with N′, and hence an additional rotation-induced predissociation mechanism. Vibrational frequencies and rotational constants are in excellent agreement with the predictions of ab initio calculations by Krossner et al., J. Chem. Phys. 101, 3973 (1994); 101, 3981 (1994). The à 2Π(A″)–X̃ 2A′ absorption shows characteristics of a transition between two Renner–Teller components and this interpretation is confirmed by careful examination of the electronic structure of the FCO ground state. Implications for assignments of absorption features at higher energy than the spectral region of the current study are discussed, and comparisons are drawn with the much studied electronic spectroscopy of both the HCO radical and the isoelectronic NO2.

Fourier transform emission spectrum of the HCSi radical, Ã 2Σ+–X̃ 2Πi transition

A Fourier transform emission spectrum of the HCSi, Ã 2Σ+–X̃ 2Πi transition was observed by means of a Schüler-type discharge tube in the 9000–14 000 cm−1 spectral region. Three bands whose origins appeared at 12 934.406, 11 766.721, and 10 752.430 cm−1 were rotationally analyzed and assigned, respectively, to the (100)–(000), (000)–(000), and (000)–(100) bands. The new ab initio calculated A(X̃ 2Π) spin–orbit constant agrees well with the experimental value. Weak rotational perturbations in the (100) level of the upper electronic state are likely due to highly excited vibrational levels of the ground state, whereas the “anomalous” increase of the spin–rotation constant in the (100) level of the ground state relative to the (000) level was shown to result of a Fermi interaction with the (020) Π2 Renner–Teller components. A comparison was made between the rotational constants of the (000) ground state level with those obtained in concomitant works.

Excited electronic states of carbon disulphide

The near-ultraviolet spectrum of CS2 is studied thoroughly using high level CISTDQ and EOM-CCSD theory with DZP and TZ2P(f) basis sets. Potential energy curves of the first seven singly excited states with respect to the SCS bond angle have been predicted. The relative energy ordering of the excited states as established at the equilibrium geometries using EOM-CCSD theory is: X˜1Σ+g, < a3B2 < b˜3A2(R) < A1A2 < c˜3B2 < B˜1B2 (V) < d˜3A2 < C˜1A2, which is at odds with previous theoretical work. The bent B˜1B2 state arises from the Renner—Teller splitting of a linear 1Δu state into 1B2 and 1A2 states. In disagreement with previous experimental predictions that the 1A2 state is the lower lying component of this splitting, it is firmly established from the high level results in this research that the C˜1A2 state is the higher lying component of this Renner—Teller pair. Equilibrium geometries are determined and shown to agree qualitatively with experiment, save for the B˜1B2 state. From an analysis of the complex rotational structure of the V band the experimental geometry of the B˜1B2 state was determined to be slightly bent (re = 1.544 Å, θe = 160°), whereas the methods employed in this research predict a significantly bent geometry (re = 1.632 Å, θe = 132.1° at EOM-CCSD/TZ2P(f)). Relative transition energies, Te, are predicted, and EOM-CCSD calculations are shown to agree well with available experimental data, and show the assignment of the V and R bands to be correct while the T band is correctly assigned to the A1A2 state and not the lower lying Renner—Teller component of the 1Δu state. The high level CI methods, although yielding qualitatively correct potential energy curves, do not provide quantitatively accurate transition energies, and it is clear that even an exhaustive treatment of the eight valence π electrons is not entirely satisfactory, while EOM-CCSD is established as an accurate method for the prediction of excited state potential curves.

Excited electronic states of carbon disulphide

The near-ultraviolet spectrum of CS2 is studied thoroughly using high level CISTDQ and EOM-CCSD theory with DZP and TZ2P(f) basis sets. Potential energy curves of the first seven singly excited states with respect to the SCS bond angle have been predicted. The relative energy ordering of the excited states as established at the equilibrium geometries using EOM-CCSD theory is: X˜1Σ+g, < a3B2 < b˜3A2(R) < A1A2 < c˜3B2 < B˜1B2 (V) < d˜3A2 < C˜1A2, which is at odds with previous theoretical work. The bent B˜1B2 state arises from the Renner—Teller splitting of a linear 1Δu state into 1B2 and 1A2 states. In disagreement with previous experimental predictions that the 1A2 state is the lower lying component of this splitting, it is firmly established from the high level results in this research that the C˜1A2 state is the higher lying component of this Renner—Teller pair. Equilibrium geometries are determined and shown to agree qualitatively with experiment, save for the B˜1B2 state. From an analysis of the complex rotational structure of the V band the experimental geometry of the B˜1B2 state was determined to be slightly bent (re = 1.544 Å, θe = 160°), whereas the methods employed in this research predict a significantly bent geometry (re = 1.632 Å, θe = 132.1° at EOM-CCSD/TZ2P(f)). Relative transition energies, Te, are predicted, and EOM-CCSD calculations are shown to agree well with available experimental data, and show the assignment of the V and R bands to be correct while the T band is correctly assigned to the A1A2 state and not the lower lying Renner—Teller component of the 1Δu state. The high level CI methods, although yielding qualitatively correct potential energy curves, do not provide quantitatively accurate transition energies, and it is clear that even an exhaustive treatment of the eight valence π electrons is not entirely satisfactory, while EOM-CCSD is established as an accurate method for the prediction of excited state potential curves.

Nonadiabatic bending dissociation in 16 valence electron system OCS

The speed, angular, and alignment distributions of S(1D2) atoms from the ultraviolet photodissociation of OCS have been measured by a photofragment imaging technique. From the excitation wavelength dependence of the scattering distribution of S(1D2), the excited states accessed by photoabsorption were assigned to the A′ Renner–Teller component of the 1Δ and the A″(1Σ−) states. It was found that the dissociation from the A′ state gives rise to high- and low-speed fragments, while the A″ state only provides the high-speed fragment. In order to elucidate the dissociation dynamics, in particular the bimodal speed distribution of S atoms, two-dimensional potential energy surfaces of OCS were calculated for the C–S stretch and bending coordinates by ab initio molecular orbital (MO) configuration interaction (CI) method. Conical intersections of 1Δ and 1Σ− with 1Π were found as adiabatic dissociation pathways. Wave packet calculations on these adiabatic surfaces, however, did not reproduce the low-speed component of S(1D2) fragments. The discrepancy regarding the slow S atoms was attributed to the dissociation induced by nonadiabatic transition from A′(1Δ) to A′(1Σ+) in the bending coordinate. This hypothesis was confirmed by wave packet calculations including nonadiabatic transitions. The slow recoil speed of S atoms in the nonadiabatic dissociation channel is due to more efficient conversion of bending energy into CO rotation than the adiabatic dissociation on the upper state surface. By analyzing the experimental data, taking into account the alignment of S(1D2) atoms, we determined the yield of the nonadiabatic transition from the A′(1Δ) to the ground states to be 0.31 in the dissociation at 223 nm. Our theoretical model has predicted a prominent structure in the absorption spectrum due to a Feshbach resonance in dissociation, while an action spectrum of jet-cooled OCS measured by monitoring S(1D2) exhibited only broad structure, indicating the limitation of our model calculations.

Raman resonance de-enhancement in the excitation profile of CS2

The total differential Raman cross section of the symmetric vibrational mode of CS2 (652 cm−1) in liquid phase has been measured as a function of excitation wavelength from the visible to the ultraviolet. The resulting excitation profile shows a strong preresonance enhancement when the excitation wavelength is less than 300 nm. The cross section measured at 240 nm is about three orders-of-magnitude larger than the ν4 dependence for Raman scattering. The observed preresonant effect appears to be dominated by the B21(Σu+1)←Σg+1 transition. A minimum in the excitation profile occurs at a wavelength that is associated with the peak of the near-UV absorption band (∼320 nm). The observed dip in the profile is ascribable to a quantum interference between the B21(Σu+1) and the two Renner–Teller components, B21 and A21(Δu1). The transition from the ground state to the lower electronic state is electronically forbidden, but it becomes vibronically allowed due to the Renner–Teller interaction. This may be the first observation of Raman resonance de-enhancement due to the interference involving three excited states.

Laser-induced fluorescence spectrum of the FCO radical

Laser-induced fluorescence spectra of FCO are reported between 29 000 cm−1 and 32 800 cm−1. FCO was prepared by three separate procedures: photolysis of CF2O and C2F2O2, and photolysis of F2 in the presence of CO. The observation of the same spectral features from all three production schemes confirms the assignment of FCO as the spectral carrier. Although the LIF spectrum lies in the same wavelength region as the UV absorption spectrum, the two spectra do not have the same appearance and so represent different upper states. The LIF spectrum is assigned as a transition to the A″ Renner–Teller component of a linear 2Π state predicted by ab initio calculations. The spectrum shows a progression of bands at approximately 430 cm−1 intervals, in good agreement with the predicted spacing of bending levels in the 2Π state. The lower frequency stretching mode ν1 occurs at approximately 960 cm−1. The vibronic bands are strongly degraded to the red, consistent with the calculated geometry of the linear state but not the bent A state to which the absorption spectrum in this region is assigned. Resolved emission from the longest wavelength prominent bandhead at 29 872 cm−1 shows progressions in the C–O stretch and bend modes of the ground state. The fluorescence lifetime of this band extrapolated to zero pressure is 95±4 ns, while that of the band at 31 136 cm−1 is 63±5 ns.

Zero-kinetic-energy photoelectron spectroscopy from the à 1A u state of acetylene: Renner–Teller interactions in the trans-bending vibration of C2H+2 X̃ 2Πu

Double-resonance excitation via the à 1Au state is used to record zero-kinetic-energy photoelectron spectra of acetylene. The analysis of these spectra leads to an improved value of 91 952±2 cm−1 for the adiabatic ionization potential to the C2H2+ X̃ 2Πu ionic ground state. Because the à 1Au intermediate state has a trans-bent geometry, transitions from it readily populate the trans-bending vibration of the ground state ion, leading to new information about this mode and its Renner–Teller interactions. The relative intensities of the Renner–Teller components and of the rotational structure within each component also provide information on the dynamics of the photoionization process.

A high-resolution analysis of the à 2A′–X̃ 2A′ transition of CaSH by laser excitation spectroscopy

The high resolution spectrum of the à 2A′–X̃ 2A′ transition of CaSH has been recorded near 650 nm using laser excitation spectroscopy with selected fluorescence detection. While both a-type and b-type rotational transitions have been observed, extensive measurements have been made for the b-type transitions up to K′a = 4 and K″a = 5. Altogether over 3000 rotational lines have been measured and fitted with an A-reduced Hamiltonian. The X̃ 2A′ state has rotational constants A=9.693 322(46) cm−1, B=0.141 864 7(33) cm−1, and C=0.139 581 0(33) cm−1. The à 2A′ state has a band origin at 15 380.284 7(2) cm−1, and effective values for the rotational constants A=9.090 808(78) cm−1, B=0.147 459 8(34) cm−1, and C=0.144 804 2(34) cm−1. An approximate r0 structure for CaSH is discussed. The à 2A′ state is the lower energy Renner–Teller component of the ‘‘à 2Π’’ state of the hypothetical linear CaSH molecule, and consequently was found to have a relatively large positive value for the spin–rotation parameter εaa at 3.445 69(26) cm−1. The upper asymmetry component of the F1 spin component of the Ka=1 stack and the F2 spin component of the Ka=0 stack in the à 2A′ state perturb each other with an avoided crossing between J=37.5 and J=38.5. These two spin components interact through the off-diagonal ‖εab+εba‖/2 element of the spin–rotation tensor. For CaSH, the à 2A′ state has ‖εab+εba‖/2=0.065 915(46) cm−1.

The dynamical Renner–Teller effect. III. Rovibronic energy transfer pathways in the NCO(X̃ 2Π)+He system

As a linear triatomic radical in an electronic state with Λ≠0 bends, the vibrationally excited levels are split as a result of vibronic interactions. This is the well-known Renner–Teller effect. Reported here is the first study of the collision-induced transitions between these Renner–Teller components. It is found that the pathways for these processes are highly selective and their efficiencies, in some cases, can compete with rotationally inelastic collisions. A simple, intuitive argument is presented to underscore the physical mechanisms for this finding. Preliminary, more rigorous theoretical analysis confirms the essential ideas of the proposed interpretations.