Femtosecond degenerate four-wave mixing of carbon disulfide: High-accuracy rotational constants

Abstract

Femtosecond degenerate four-wave mixing (fs-DFWM) rotational coherence spectroscopy (RCS) has been used to determine the rotational and centrifugal distortion constants of the 00 (0)0 ground and 01 (1)0 vibrationally excited states of gas-phase CS(2). RCS transients were recorded over the 0-3300 ps optical delay range, allowing the observation of 87 recurrences. The fits yield rotational constants B(00 (0)0)=3.271 549 2(18) GHz for (12)C(32)S(2) and B(00 (0)0)=3.175 06(21) GHz for the (12)C(32)S(34)S isotopomer. The rotational constants of the degenerate 01 (1)0 bending level of (12)C(32)S(2) are B(01 (1)0)=3.276 72(40) and 3.279 03(40) GHz for the e and f substrates, respectively. These fs-DFWM rotational constants are ten times more accurate than those obtained by CO(2) laser/microwave heterodyne measurements and are comparable to those obtained by high-resolution Fourier transform infrared spectroscopy. Ab initio calculations were performed at two levels, second-order Moller-Plesset theory and coupled-cluster singles, doubles, and iterative triples [CCSD(T)]. The equilibrium and vibrationally averaged C=S distances were calculated using large Dunning basis sets. An extrapolation procedure combining the ab initio rotational constants with the experiment yields an equilibrium C=S bond length of 155.448 pm to an accuracy of +/-20 fm. The theoretical C=S bond length obtained by a complete basis set extrapolation at the CCSD(T) level is r(e)(C=S)=155.579 pm, or 0.13 pm longer than that in the experiment.

Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type

“…ab initio methods to determine a semiexperimental structure by linear basis-set extrapolation, as has been described earlier for symmetric-top molecules for which only one rotational constant is experimentally accessible. [1][2][3]17,19,20,48 In short, a structural parameter r (bond length, bond angle) is calculated using highly correlated ab initio calculations, e.g., the CCSD(T) method using a systematic series of basis sets, e.g. the Dunning correlation-consistent weighted core-valence polarized basis sets series cc-pwCVXZ, where X = 2, 3, .…”

“…We find evidence for a new type of rotational transient, denoted S-type. By combining the experimental rotational constants with coupled-cluster CCSD(T) calculations using large basis sets, we have determined the semiexperimental 1,[17][18][19][20] independent structure parameters of p-DFB, i.e., the C 1 -C 2 , C 2 -C 3 , C-F, and C-H bond lengths and two bond angles.…”

Accurate determination of the structure of 1,3,5-trifluorobenzene by femtosecond rotational Raman coherence spectroscopy and ab initio calculations

“…(1). P J;K is modeled according to the exponential gap law for collisional rotational energy transfer (RET), which has been successfully applied previously [38,39,42]. The probability for a transfer from a rotational state J; K into translational energy is P J;K ¼ a Á e ÀcDE J;K where a and c are coefficients to be fitted [53].…”

“…Simulations of fs-DFWM transients [38,39] as well as the underlying theory [43][44][45] are well established and are therefore only briefly reviewed. Three degenerate laser beams are focused in a forward box configuration into a Raman-active medium.…”

“…Femtosecond degenerate four-wave mixing (fs-DFWM), a Raman scattering type of rotational coherence spectroscopy (RCS) [21][22][23] permits the determination of rotational and centrifugal distortion constants of the ground state [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], and, when thermally populated, of low lying vibrational levels [41,42]. Here, we present an application of fs-DFWM rotational coherence spectroscopy to obtain highly accurate rotational and centrifugal distortion constants of the ground vibrational state and of the m 10 ; m 23=24 ; m 29=30 and 2m 10 vibrationally excited states of TFB.…”