On the Renner−Teller Effect and Barriers to Linearity and Dissociation in HCF(ÃA‘ ‘)

Abstract

To further investigate the Renner−Teller effect and barriers to linearity and dissociation in the simplest singlet carbene (HCF), we recorded fluorescence excitation spectra of the pure bending transitions with n = 0−7 and the combination bands with n = 1−6 and with n = 0−3 in the HCF Ã1A‘ ‘ ← X̃1A‘ system. The spectra were measured under jet-cooled conditions, using a pulsed-discharge source, and rotationally analyzed to yield precise values for the band origins and rotational constants. The derived Ã-state parameters are in excellent agreement with the predictions of ab initio electronic structure theory. The approach to linearity in the à state is evidenced in a sharp increase in the rotational constant A, as first reported by Kable and co-workers, and a minimum in the vibrational intervals near the 27 level. A fit of the vibrational intervals for the pure bending levels yields a barrier to linearity of 6300 ± 270 cm-1 above the vibrationless level. Our observation of the K a‘ = 1 level of 1126 places a lower limit on the à state barrier to dissociation of ∼ 8555 cm-1 above the vibrationless level.

Electronic spectroscopy of the system of CDCl

“…The apparatus, pulsed discharge nozzle, and data acquisition procedures are identical to those used in previous studies of CHF, CDF, CHBr, CDBr, and CHCl [8,[44][45][46][47][48][49][50][51][52][53][54], and, therefore, only the important differences will be highlighted. The carbene CDCl was produced using a pulsed electrical discharge through a $1-2% mixture of CD 2 Cl 2 (Cambridge Isotope Labs, 99.9 atom % of D) seeded in high purity He.…”

“…Building upon the seminal work of Merer and Travis in the 1960's [9,10], and later work from the groups of Hirota [11][12][13][14][15][16][17][18], Sears [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], Kable [34][35][36], and Chang [37][38][39][40][41][42][43], our group has recently undertaken a systematic study of the monohalocarbenes CHF, CHCl, CHBr and their deuterated isotopomers, using a variety of methods including fluorescence excitation spectroscopy, lifetime measurements, polarization and Zeeman quantum beat spectroscopy, and single vibronic level emission spectroscopy [8,[44][45][46][47][48][49][50][51][52][53][54]. Most recently, we reported comprehensive surveys ...…”

“…Most recently, we reported comprehensive surveys of theà 1 A 00 X 1 A 0 system of CHBr, CDBr, and CHCl using fluorescence excitation and single vibronic level (SVL) emission spectroscopy [8,53,54]. In each case we recorded and analyzed many new cold bands, and reported the first measurement of theà 1 A 00 state C-H stretching frequencies following the observation of bands in the progressions 1 1 0 2 n 0 and 1 1 0 2 n 0 3 m 0 [36,46,52]. Exploiting these as pump transitions in SVL emission spectroscopy, we examined the vibrational level structure up to $9000 cm À1 above the vibronic origin ofX 1 A 0 , reporting many previously unobserved levels in both theX 1 A 0 and a 3 A 00 states and probing spin-orbit mixing in these systems in new detail.…”

Spectroscopic Study of the Ã1A" - X~1A' System of CHBr

“…A considerable number of spectroscopic investigations have provided detailed experimental information on the ground and first excited singlet states ( A" for the unsymmetrical molecules) of the monohalocarbenes and dihalocabene. [1][2][3][4] The methylene radical has a triplet ground electronic state ( 3 B 1 ), 5 while all of the mono-and dihalogenated derivatives have singlet ground states ( 1 A 1 for the symmetrical dihalocarbenes). Considerable information is now available on the electronic transition to the first excited electronic state ( 1 B 1 ) of a number of halocarbenes, and vibrational energies and rotational constants in both ground and excited electronic states have been determined.…”

“…Considerable information is now available on the electronic transition to the first excited electronic state ( 1 B 1 ) of a number of halocarbenes, and vibrational energies and rotational constants in both ground and excited electronic states have been determined. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This has allowed determination of molecular geometries and information on the relevant potential energy surfaces. The 1 A 1 and 1 B 1 states coalesce to a degenerate electronic state at linear geometry, thus leading to the Renner-Teller effect which couples the two states.…”